These are words you don't want to see associated with your favorite bat. Baseball and softball leagues have bat standards set by governing bodies that dictate what bats are acceptable for use. To become certified, bats must pass tests conducted by independent labs, which is what BBCOR Certification and USABat Standard use. When a bat passes the independent test, the bat manufacturer is notified, and the corresponding certification stamp can be placed on the bat.
And when a bat doesn't pass? That's when the bats are deemed illegal or banned.