In tennis if I serve the ball and it goes into the opposite service box, but hits the net on the way, it is a let.
Is there such a thing as a let in table tennis?
The table-tennis version of a tennis 'let' is sometimes called a 'net.' In general, a 'let' in table tennis is when the rally is stopped for some reason and no point is awarded. Examples of Lets include
18.104.22.168 if in service the ball, in passing over or around the net assembly, touches it, provided the service is otherwise good or the ball is obstructed by the receiver or his/her partner;
22.214.171.124 if the service is delivered when the receiving player or pair is not ready, provided that neither the receiver nor his/her partner attempts to strike the ball;
126.96.36.199 if failure to make a service or a return or otherwise to comply with the Laws is due to a disturbance outside the control of the player;
188.8.131.52 if play is interrupted by the umpire or assistant umpire.
184.108.40.206 if the receiver is in a wheelchair due to a physical disability and the ball
220.127.116.11.1 after touching the receiver’s court returns in the direction of the net;
18.104.22.168.2 comes to rest on the receiver's half;
22.214.171.124.3 in singles leaves the receiver’s half after touching it by either of its sidelines.
These are taken from the USA Table Tennis rules, but the ITTF rules are basically the same.