[MCBear]

tornado, which rule set do you want the definition to cover - NFHS, USAV, NCAA/NAIA/NJCAA, or AAU????

NFHS Rule 9.4.5 defines "Legal contact is a touch of the ball by a player's body above and including the waist which does not allow the ball to visibly come to rest or involve prolonged contact with a player's body."

USAV Rule 10.2 describes the characteristics of the hit
"* 10.2.1 The ball may touch any part of the body.
* 10.2.2 The ball must be hit, not caught and/or thrown. It can rebound in any direction.
* 10.2.3 The ball may touch various parts of the body, provided that the contacts take place simultaneously.
Exceptions:
** 10.2.3.1 At blocking, consecutive contacts may be made by one or more blocker(s) provided the the contactgs occur during one playing action.
** 10.2.3.2 At the first hit of the team, the ball may contact various parts of the body consecutively provided that the contacts occur during one action.
** USAV 10.2.3.2 The first hit of the team includes reception: (a) of the serve; (b) of an attack-hit by the opponent (this may be a soft or hard attack-hit); (c) of a ball blocked by one's own team and (d) of a ball blocked by the opponents. During the team's first hit, successive contacts with various parts of the player's body are permitted in a single action of playing the ball. These include contacts involving "finger-action" on the ball and contact with the foot. The ball, however, may not be caught and/or thrown."

Hopefully, these two rules will answer your question.