Back in the days, the slot machines of the period had just three reels and a single payline. Slots of these days, in contrast, have from 1 to 50 paylines, with a few slots even having above 50 paylines.
However, playing with the maximum number of available paylines can be expensive. With that being the case, some slots feature a flexible number of paylines, so that players can make use of as much paylines as they feel a need for.