What is a false path timing constraint?
False paths are timing paths that will never really be exercised in the final design. Suppose you are designing a 4-bit counter and it turns out that there is a very slow delay path when incrementing from 12 to 13. If your design always resets the counter whenever the count equals 9 then that slow path will never be seen in the actual design. You label the slow path as a false path so that the compiler doesn't spend any time, or add any extra logic, in an effort to make the false path run faster.