This article is from the Table Tennis (Ping Pong) FAQ, by firstname.lastname@example.org with numerous contributions by others.
5.1 a "rally" is the period during which the ball is in play.
5.2 a "let" is a rally of which the result is not scored.
5.3 a "point" is a rally of which the result is scored.
5.4 the "racket hand" is the hand carrying the racket.
5.5 the "free hand" is the hand not carrying the racket.
5.6 a player "strikes" the ball if he touches it with his racket, held
in the racket hand, or with his racket hand below the wrist.
5.7 a player "obstructs" the ball if he or anything he wears or
carries, touches it in play when has not passed over his court or
an imaginary extension of his end line, and where it has not
touched his court since last being struck by his opponent.
5.8 the "server" is the player due to strike the ball first in a rally.
5.9 the "receiver" is the player due to strike the ball second in a
5.10 the "umpire" is the person appointed to decide the results of each
5.11 The "Assistant Umpire" is the person appointed to assist the
5.12 The stroke counter is the person appointed to count strokes under
the expedite system.
5.13 Anything that a player "wears or carries" includes anything that he
was wearing or carrying at the start of the rally.
5.14 The ball shall be regarded as passing "over or around" the net if
it passes under or outside the projection of the net assembly
outside the table or if, in a return, it is struck after it has
bounced back over the net.
5.15 The part of the playing surface nearest the server and to his right
shall be called the server's right hand court, and to his left the
server's left hand court. The part of the playing surface on the
other side of the net from the server and to his left of the center
line shall be called the receiver's right hand court, and on the
server's right the receiver's left hand court.