Offline slots were invented around a hundred years ago and today make up the majority of the gaming sector, both online and offline. Essentially a slot machine is a game in which you bet on the outcome of several spinning wheels. The wheels have pictures depicted on them; they spin; the outcome determines if you have won or not. There are today a grand variety of slots, and not just slot games but types of slots. You can find online slots with 3, 5 or 7 reels. You can also find video slots that will enable you to play up to 100 paylines per spin – this means that for each hit of the "spin" button you could play 100 times; you will also find games that take different denominations of coins and different numbers of coins.

Last but not least, online slots may have progressive jackpots. These are inflated jackpots that are paid into by a number of different machines all running the same game; thus a game that's being played in one casino by 100 people and in another casino by another 100 will all be paying a small amount of their stake into one jackpot. This is how these progressive jackpots get so big, and often reach the hundreds of thousands of dollars. Every person playing on a progressive jackpot game is in with a chance of winning this enormous jackpot. 

The reason that so many people are attracted to playing online slot games is because it's so easy. Not only is it not complicated, but there are literally no rules at all to learn – you enter the site, pick a game and hit "spin". In addition to the ease of play, the slots are very fast moving and thus incredibly exciting, plus of course especially in the case of progressive the possibility of such large wins is a huge attraction.