You must stand behind the base line.
The base line, the line in the back.
Everywhere in your court!
You should stand behind the line, to serve a volleyball. If you put one of your legs over the line, the serve won't count.
a service fault in tennis is when you either when you serve and you don't get it over the first line OR you get it out
In professional tennis, there are line judges for that. In non-professional tennis, however, a server can call his or her own serve out. Most do not because it is a point against them, even though the opponent thought the serve was in.
In tennis, it is a foul if you step over the line while serving.
In singles you can serve to any part of the table. In doubles you can only serve to/from the right court. If the ball touches the line, it is in.
If any part of the ball is touching the line, but the rest is out, it is still called in.
It is the line you stand behind when you serve. It is the one in the way back.