For Reference Only, but I think the definitions listed are current for the respective sanctioning bodies listed.
USA Softball
A pitched ball that is intentionally tapped with the bat, slowly, within the infield. It is not a bunt attempt if the bat is held in the strike zone.
USSSA
An attempted bunt (“offer”) is any movement of the bat toward the ball when the ball is over or near the plate area. Holding the bat in the strike zone is considered an attempt to bunt. In order to take a pitch, the bat must be pulled back away from the ball. If an attempted bunt results in a foul ball, it is treated as any other foul ball, if the batter has two strikes and this happens, the batter is out
NSA
Any non-swinging movement of the bat intended to tap the ball into play. The mere holding of the bat in the strike zone is considered a bunt attempt no matter the placement of the pitch. To take a pitch the batter must withdraw the bat away from the ball
NCAA
A legally batted ball not swung at but intentionally tapped with the bat. A bunt attempt is any non-swinging movement of the bat intended to tap the ball into play. Holding the bat in the strike zone is considered a bunt attempt. In order to take a pitch the bat must be withdrawn -- pulled backward and away from the ball.
NFHS / PGF
A bunt is a legally batted ball not swung at but intentionally tapped with the bat. An attempted bunt is any non-swinging movement of the bat intended to tap the ball into play. Holding the bat in the strike zone is considered a bunt attempt. In order to take a pitch, the bat must be pulled back and away from the ball