A Game Over is a common term in video games, usually signifying the player losing and choosing not to continue.
When the player loses a fight, they are treated to a defeat screen, whose appearance varies based on the game. The game will then cut to a "Continue?" countdown. In most cases, the announcer counts down from "9" to "0", and the player has that much time to insert more coins and then press the Start button to continue (in the arcade versions, inserting a coin resets the countdown back to 9, which grants a time extension, whereas in the home and portable versions, all the player has to do is to press the Start button). The countdown can be sped up by pressing buttons other than the "continue" button(s).
If the player continues, their character will be "healed", or recover, and be able to fight again, or, alternatively, the player can choose a different character. If the player does not continue, they are treated to the Game Over screen, and can submit their initials for the high-score leaderboard, depending on the game. In rare cases, losing against the final boss and choosing not to continue will result in a bad ending.
However, upon successfully beating the game, in some cases, after their character's ending plays, they may also get the Game Over screen, and be asked to submit their initials for their high score if they score high enough, depending on the game.