A payline is a sequence on the reels that usually requires matching symbols to land on in order for the game to win. With newer slot games, these are also not always lines. Some games have ‘paylines’ that require three or more matching symbols to merely be adjacent. Not much of a line, is it? However, paylines that are set on slot games remain consistent, no matter how many spins you make.
Paylines are predetermined by the game developer before the release of the game. They can take the shape of anything, from a straight line to a V shape. All that matters is that matching symbols land on a payline. You can find all of the paylines in the information section of slot games and you should look through them before playing.
Remember, a lot of games allow you to choose how many lines you would like to play, but for the most enjoyment, all lines should be played.