system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: On a DVD remote, why is the pause button symbolized by two lines? What about play and stop? (Sideways triangle and square, respectively.)
gpt
The symbols used for play and stop originated with reel-to-reel tape decks. There were forward and reverse directions and the arrow indicated which direction the tape was moving. The square indicated no tape direction because it wasn't moving. Generally, when playing audio tape the tape went from left-to-right, so the symbol pointing from left to right became the play symbol.

On devices that recorded, there'd typically be a little red light above the record button which later was represented with a red circle, and sometimes just a circle.

When cassette tapes were developed, one of the manufacturers (I think they were later bought by Teac), figured that it should be possible to pause a tape while recording. The pause feature would hold the head against the tape and have it ready to go immediately when the pause was released - it also avoided recording a sort of audio noise associated with starting a the recording mid-way through the tape. By that time, the other symbols were well known and widely used and a designer was given the task to develop a symbol for the pause function. Deciding that a pause was "like a stop", they started with the stop symbol and simply decided to break it in two. They used a vertical break rather than a horizontal one because they figured if it looked like an equals sign, people might be confused.

Enter DVDs and media keyboards. Many people haven't seen a reel-to-reel audio tape recorder except in old movies. The notion of a "direction" to the media doesn't even exist anymore. However, the meaning of the symbols for play, record, stop, and pause (and their variants) are still widely used and understood.