Answer:  A basic distinction is the following.  An enduring third party is similar to a major party in that it endures over an extended period of time.  Recent and contemporary examples include the Socialist, Communist, Prohibition, Libertarian, and Green parties.would.   Since for all sort of reasons that we have discussed, third parties don't do well in the American electoral environment, such parties (unlike major parties) really aren't trying to win elections but are interested in expressing some particular ideology or issue positions, perhaps with some hope that their views will become more popular in the future.  A flash third party is one that arises in the context of a particular election; it may have a significant impact in that one election (conceivably even win it), but then it quickly disappears.  Typically a flash third party is actually a faction that temporarily breaks off from one of the two major parties (usually as a result of some divisive issue that splits the party) and runs its own Presidential candidate (1912, 1924, 1948, 1968, maybe 1980).  The Perot candidacy in 1992 and 1996 had some of the characteristics of a flash third party, though it did not result from a split in either major party.
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Question: What does a  pre-primary endorsement by a political party refer to?

Answer:  Some states allow official party body (e.g., state or country party central committees) to endorse a candidate for office prior to the primary election (and then to use its resources to help such a candidate win the primary election and nomination).  However, most states prohibit such pre-primary endorsements by parties.
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Question:  What is the 2/3 rule at Democratic national conventions?

Answer:  From 1832 through 1936, the rules of the Democratic convention required that a candidate be supported by 2/3 of the delegates (rather than a simple majority) into order to receive the party's Presidential nomination.  (This is mentioned in passing in E&W, p. 198.)  The effect was to give each major faction or region (in particular the South) at the convention a veto over Presidential nominees.  It also could lead to bitterly deadlocked conventions that ultimately would have to nominate weak dark house candidates (see below).  The most extreme example was the 1924 convention, which ran 124 ballots (over a period of several weaks) before giving 2/3 support to John W. Davis -- a conservative Wall Street lawyer who had no electoral experience and who was devastatingly defeated by Republican President Calvin Coolidge in the Fall election.  (Historical footnote: thirty years later, Davis was the lead lawyer for the defendants in the Brown v. Board of Education supreme court case, i.e., for the southern states with segregated school systems.)
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Question:  What are dark horse candidates?

Answer:  Dark horse candidates for Presidential nominations played a significant role in the party-dominant system and (to a lesser extent) in the mixed system of Presidential nominations (but have disappeared in the present candidate-dominant system).  In the earlier eras, conventions often deadlocked after several ballots.  Then party leaders/bosses would look around for a compromise candidate acceptable to the deadlocked party factions, who might then be nominated on a subsequent ballot.  Such a candidate was called a "dark horse."  (I guess the term comes from horse racing.)
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Question:  What were some of the characteristic of the "mixed system" of major-party Presidential nominations that prevailed from 1912 through 1968?

Answer:   In the 19th century (the era of the party-dominant nominating process), Presidential nominating conventions were dominated by the party leaders who selected the delegates from their states and, for the most part, controlled their votes.  Thus the only way for ambitious politicians to seek their party's Presidential nomination was to appeal to these "party bosses," and the question of who would be the nominee was settled at the convention.   The introduction of Presidential primaries in the early 20th century (in some states -- by no means all or even most) was intended to reduce the power of these party "bosses" and to some extent had the intended effect.  Such primaries, coupled with the development of a national mass media (mass circulation national magazines, radio, and then television), allowed politicians seeking their party's President nomination the opportunity to appeal directly to rank and file voters (rather than to the "bosses"), so primaries made an outsider strategy feasible in seeking a Presidential nomination.  At the same time, because most states did not have primaries, prospective Presidential candidates also had the option of pursuing an insider strategy of not entering primaries, hoping that the candidates who did enter primaries would "kill each other off," and then seeking the support of bosses in the 19th century manner.  (In the party-dominant system, only the insider strategy was available.  Making the outsider strategy available as well created the "mixed system.")  The second revolution in Presidential nominations took place between 1968 and 1972 when (for various reasons) almost all states adopted Presidential primaries (or open caucus systems, such as in Iowa, that operate much like primaries), resulting in what is called the candidate-dominant system.  Now there really are no party leaders controlling blocks of votes at the conventions, and all prospective candidates must pursue outsider strategies and run in as many primaries as possible (also see see below on "front-loading").
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Question:  What are the different types of Presidential primaries?

Answer:   There is great variation from the state in they way they organize Presidential primaries (and states often change their rules from one election year to the next).  Under the mixed system of Presidential nominations (1912-1968), one could distinguish among three broad types.  Delegate-selecting primaries: voters actually vote for the delegates who would go to the convention; often (but not always) candidates for delegate would be clearly pledged to one or other Presidential candidate (like candidates for Presidential elector in the general election), so voters could (indirectly but meaningfully) express preferences for contestants for the party's Presidential nomination.  Delegate-instructing primaries: voters directly express preferences for Presidential candidates running in the primary; while the delegates are otherwise selected, they are bound to vote at the convention (at least on early ballots) according to the results of the primary.  Beauty-contest primaries: in what is in effect a large-scale public opinion poll, voters directly express preferences contestants for the party's Presidential nomination  but the results have no binding effect on who the delagates are nor how they will vote.  While the details of primary rules still vary from state to state in the present candidate-dominant system, the upshot is that voters in almost every state can directly express preferences among Presidential contestants and that Presidential candidates win delegate votes roughly proportional to how well they do in each primary (the latter point being more clearly true on the Democratic side than the Republican).
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Question:  What is front-loading of Presidential primaries?

Answer:  Presidential primaries are scheduled by state legislatures over a window that traditionally extended from early February to mid-June.  Under the mixed system of Presidential nominations, the (relatively small number of) primaries were spread fairly evenly over this interval.  In particular, some states (especially California) seemed to benefit from having primaries late in the season, since typically many candidates would already have been knocked out (having done poorly in earlier primaries) leading to a showdown between two remaining candidates in the last primaries that might well decide the nomination.  However, since the number of states holding primaries exploded after 1968, nominating contests have usually been decided well before the last primaries.  Thus the states holding late primaries have an incentive to move them earlier in the season, with the result that nomination contests are decided even earlier.  Given the general perception that the first primaries are the most important, states have been moving their primaries earlier and earlier, resulting in front-loading in which most primaries take place in a short period of time early in the primary season.  Evidently, such front-loading will be more pronounced in 2004 than ever before.
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