A semifinal is a game or match that is played to decide who will play in the final game or match.
A semifinal can be very exciting because the winner gets to play in the final game or match.
Examples:
The semifinal is tomorrow.
She won the semifinal and will play in the final.
The team is practicing for the semifinal.
I hope we win the semifinal and get to play in the final!
The semifinal is the most important game before the final.
The semifinal is where we have to win to get to the final.