Both as a noun and a verb, bloat refers to being swollen, puffed up, or overfilled. You can bloat something by filling it up to the point where it swells.
You use bloat to make the point that something is more than just fat or large — it's too puffed up or swollen and seems like it might burst. Most often you'll see bloat used to describe things that are filled up with liquid or gas — as in that feeling you get after eating too much. But you might also see the meaning extended to include things like budgets, egos, and expensive shoe collections. Anytime someone has way too much of something, you might see bloat used to describe the situation.