Bail can mean a few different things. First, it can refer to a skater landing safely on his or her feet after failing at a trick. It can also mean something along the lines of "chickening out", where a skater gives up on a trick halfway through and lands on his or her feet. Third, it is often used for a crash or failed trick where the skater does not catch his or her feet, and gets hurt - often painfully and / or humorously.
Many popular skateboarding videos will have a "bails" section where you get to watch your favorite pros beat the crud out of themselves while falling off their skateboards. In fact, the earlier Tony Hawk Pro Skater video games had "Bails" videos that you could unlock where you could see pros racking themselves on poles, smashing their faces into sidewalks, and tumbling down concrete stairs. Good clean family fun.
Read people's Worst Skateboarding Bails Stories to get a better idea of what constitutes a "bail", or share your own story!
Also Known As: crashing, falling, chickening out, etc.
Examples: Tami tried to ollie off the balcony but ended up bailing and landing in a bush.