Prone
Source Player Core pg. 439
You're lying on the ground. You are off-guard and take a –2 circumstance penalty to attack rolls. The only move actions you can use while you're prone are Crawl and Stand. Standing up ends the prone condition. You can Take Cover while prone to hunker down and gain greater cover against ranged attacks, even if you don't have an object to get behind, which grants you a +4 circumstance bonus to AC against ranged attacks (but you remain off-guard).
If you would be knocked prone while you're Climbing or Flying, you fall. You can't be knocked prone when Swimming.
If you would be knocked prone while you're Climbing or Flying, you fall. You can't be knocked prone when Swimming.