A narrow notch, groove, or opening, as in a keyway in a piece of machinery or a slot for coins in a vending machine. Also: a position in a group, series, or sequence; an allotment of time, money, or other resource. From Webster’s New World College Dictionary, 4th Edition. Copyright 2010 by Houghton Mifflin Harcourt. All rights reserved.

Originally, casinos installed slot machines as a diversion for casual gamers. They were relatively easy to operate and required very little gambling knowledge. As they became more popular, they moved off the sidelines and into the spotlight, eventually generating more than 60 percent of annual gaming profits in the United States alone.

While slots have changed a lot over the years, their basic operation remains the same. Players pull a handle to rotate a set of reels with printed pictures on them, and winning or losing depends on which pictures line up with the pay line, a line running through the middle of the viewing window. Some machines have multiple pay lines, and the amount you win — called a payout — varies according to which ones land. In addition, many modern video slots feature pay both ways and adjacent pays, which increase their max win potential. There are also a number of variations on the classic game, with manufacturers creating games based on television shows, poker, craps and horse racing, among other things. Many of these have interesting features that make them unique.