A cheese ship is could also defined as any ship that requires little basic pilot skill to fight with. Good examples are the Cavalier or drone ships. At the most basic level, the player has little actual fighting to do, since most of his weapons are controlled by the AI (fighters, drones). However, using either effectively can require great skill. A cheesy player will take such a ship because he or she doesn't know or wish to learn tactics.
A determination of cheese is also best not left to a new player; they don't have the experience or the tactics knowledge to make an accurate determination.
X ships in general are cheesy. The reason this is is that you can generally run at maximum speed with one, while charging weapons, and with ECM. These ships do not require power management skills in general, and therefore don't require the same level of skill to employ. Thus cheese. Questionable design decisions also make this worse. The MIRV rack is an excellent example. This missile exists in SFB, however, it can only fire anti-fighter missles, not missiles that can effectively attack ships. I generally refuse to play on OP D2 servers because of X ships; I don't like them, but once they're available everyone must have one to stay on the same level.
Escorts are considered cheese because Taldren in a very questionable design decision decided that the G missile rack would have an offensive and defensive function at the same time. The source game that SFC is taken from required you to pick the function (offensive or defensive) and switching took time. Since the game is balanced with that in mind, the change in SFC makes escort ships overpowered for their size. Not only do they escort, they also are drone cruisers at the same time. The implimentation also adds a internal for every G rack a ship has, which it did not have in the source game. It could also be said that any ship with a large number of G racks is cheesy for this reason as well.