When you have to play a backhand in tennis, the backside of your hand is facing the court.
Before rackets where introduced in tennis, players would play with their hands, that's why we still use that term.
A backhand stroke is when you hit the bal with your non dominant side. for example: if you are right handed and you have to hit the ball on your left side.
There are two types of backhands: two handed and one handed backhands.
• Two handed backhand: you use two hands to hold your racket while playing a backhand
• One handed backhand: you only use one hand to play a backhand