Neoconservatism: An essay on the loaded term by the man for whom, arguably, it was coined, Irving Kristol:

What exactly is neoconservatism? Journalists, and now even presidential candidates, speak with an enviable confidence on who or what is "neoconservative," and seem to assume the meaning is fully revealed in the name. Those of us who are designated as "neocons" are amused, flattered, or dismissive, depending on the context. It is reasonable to wonder: Is there any "there" there?

He gives a good answer, though for my money he's overthinking it. Ronald Reagan gave the essential definition of a neoconservative when he explained why he was no longer a Democrat. The party, he said, "left me." (This is likely true of Kristol as well, though he doesn't say so.) Kristol rightly recognizes Reagan as a neo hero of sorts, though he then confuses matters with this statement:

Neocons do not like the concentration of services in the welfare state and are happy to study alternative ways of delivering these services. But they are impatient with the Hayekian notion that we are on "the road to serfdom." Neocons do not feel that kind of alarm or anxiety about the growth of the state in the past century, seeing it as natural, indeed inevitable. Because they tend to be more interested in history than economics or sociology, they know that the 19th-century idea, so neatly propounded by Herbert Spencer in his "The Man Versus the State," was a historical eccentricity.

Yikes, don't tell Reagan, who was a student of economics and had a pretty major problem with the "natural expansion of government" mindset. No, it is in the projection of power that the neos and Reagan met:

Finally, for a great power, the "national interest" is not a geographical term . . . A smaller nation might appropriately feel that its national interest begins and ends at its borders, so that its foreign policy is almost always in a defensive mode. A larger nation has more extensive interests . . . Barring extraordinary events, the United States will always feel obliged to defend, if possible, a democratic nation under attack from nondemocratic forces, external or internal.

For such reasons, the term neoconservative will always suffer inadequacy and surfeit at the same time. Inadequacy in that it cannot convey the nuance of opinion among modern conservatives; surfeit in that there will always be more uses of the term than are valid (as with those to whom neo means Jew or intellectual or former liberal). Really, all it was intended to designate, I presume, was a "new" conservative. Such a conservative had to come from somwhere, since we aren't born with fully formed political platforms in our brains. The new conservatives were those who saw liberalism in America increasingly sympathetic toward European-style socialism, increasingly playing the Soviet apologist, and increasingly suspicious of the motive of national interest. Thus the neo-con can be, as he is in the minds of the NYT editorial board, an East-coast, intellectual Jew. But he is also a heartland-bred child of poverty, like Reagan. Or a military family scion like John McCain. Even Joe Lieberman spouted an essentially neoconservative message (generally pro-business, suspicious of affirmative action, tough on crime, pro-voucher, free-trader, internationally hawkish, pro-SDI, Bill Bennett-style moralist -- Jesus, are you sure he's a Democrat?) until he developed his national-office aspirations.

Point is, neoconservative originally described a change of position, not necessarily a position itself, much the way the term New Democrat floats around now, comprising people as distinct as John Breaux (sits with Lieberman on the spectrum) and Al Gore (who seems to drift left by the day).