An equaliser is a term used in association football

Football (soccer)

Association football, more commonly known as football or soccer, is a sport played between two teams of eleven players with a spherical ball...

 and ice hockey

Ice hockey

Ice hockey, often referred to as hockey, is a team sport played on ice, in which skaters use wooden or composite sticks to shoot a hard rubber puck into their opponent's net. The game is played between two teams of six players each. Five members of each team skate up and down the ice trying to take...

, sometimes in baseball

Baseball

Baseball is a bat-and-ball sport played between two teams of nine players each. The aim is to score runs by hitting a thrown ball with a bat and touching a series of four bases arranged at the corners of a ninety-foot diamond...

 to describe a goal

Goal (sport)

Goal refers to a method of scoring in many sports. It can also refer to the physical structure or area of the playing surface where scoring occurs....

 or run

Run (baseball)

In baseball, a run is scored when a player advances around first, second and third base and returns safely to home plate, touching the bases in that order, before three outs are recorded and all obligations to reach base safely on batted balls are met or assured...

scored by one particular team that ties the game.

For example, if Team A is winning 1-0 against Team B, but then Team B scores and makes the match 1-1, then that goal would be deemed an equaliser.

It is a well recognised term and quite often used during commentary.