What does the term 'booked' mean in soccer?

Answer 1

If a player commits a foul which is worthy or either a yellow or red card, he is 'booked' whereby the referee writes the players details and details of the foul in his notebook to be reported to the governing body

Answer 2

A booking is when you are written into the referee's book. It's a another word for receiving a card. (Usually a yellow card.)