I think you are referring the button that user interface provides when such operations are executing.

When the file is playing, you want to pause it, then you may press the pause symbol (Two vertical lines) button to pause it, or else press the play symbol (sideways triangle) to continue playback of the file.

To explain why the pause symbol is two vertical lines, and the play symbol the sideways triangle, here're some history:

the pause button indicates the two rollers beside the read OR write magnet on a tape deck that push the tape up against the head. the single vertical bar with triangle indicates one roller retracted faster play in that direction... basically other than the "play" symbol, which simply means "go" the rest of the symbols are based on the state of the controlling rollers. Record was a red circle, indicating the red shelled "studio in use recording" light outside the door.

The vertical lines represent the sides of frames on a reel. Pause means you are stopped between two frames, play means you are moving through the frames left to right (hence the arrow), fast forward is moving through the frames at some multiple of 1x, and the scene skip button pushes you forward to some preset "hard" frame edge.

From https://ux.stackexchange.com/a/90343