Bartop is a common arcade game form factor.
Bartop machines have become very popular lately. They are small games designed to sit on the top of a bar or table. Most of these machines use a touch screen for control, and have multiple games inside them to choose from. The Merit Megatouch seems to be the most popular bartop available, but there are many others, and they have little real difference between them.
Your standard bartop will usually have an assortment of card games, several different trivia games, and a few puzzle games. Standard action games are usually unavailable due to the poor control afforded by a touch screen. Many bartops will also have several adult titles, whcih will either be in the form of a "Sex Trivia" game, or will be some sort of puzzle game that reveals a naughty picture when you win.
These bartops seem to currently be the biggest money makers in the arcade business, or at least they provide the biggest bang for your buck. At only a quarter a play, they can easily bring in $500 a month in a good location. They are only about $2000 new, so that means they can pay for themselves in a matter of months, after that it is just free money. If you are looking to make money from arcade games, then bartops are the way to go (a hot new racing title may bring in $1000 a month, but that machine is going to cost you $10,000, so clearly bartops are the wiser investment).
I do not really recommend purchasing a bartop for home use. They are expensive on the used market (when compared to standard upright machines, and really don't have much to offer in the way of compelling gameplay. Sure, your average bartop may have 25 games inside, but those games are just as good as some of the freeware titles you can play on your computer. For a home multi-game I would recommend a JAMMA cabinet, or possibly a MAME cabinet, you will get a lot more for your money that way.