Huck is a common term in the game of ultimate that refers to a long throw downfield, often all the way into the endzone. It is somewhat similar to the term bomb in (American) football.
Huck can be used as a noun ("Did you see that beautiful huck") or a verb ("They have no strategy, they just huck every time"). Huck refers to the intention of a throw rather than its actual form. A huck can be forehand or backhand. On occasion, strong players have even been known to throw a huck as a hammer. Pull, on the other hand, is also a long throw, but this refers specifically to the initial throw to start a point (similar to a kickoff).
From a strategic perspective, hucks can be a very powerful weapon, especially if the offense has the wind at their back. However, at the higher levels of ultimate, where defense is better, shorter throws, with a higher chance of completion are favored. The major exception to this is when players find themselves being poached (ignored by their defender). Even at the beginning levels though, constant hucking is sometimes frowned upon because it doesn't teach the requisite strategies for high-level ultimate.