A dedicated cabinet is an arcade game that came out of the factory as a specific game, (and is still the exact same game).
In the earliest days of arcade games almost all games came in a dedicated cabinet. These things were usually works of art. The early games would be covered almost completely in painted graphics, (the industry later started using stickers).
But most of these games were ruined by the process of conversion. When that original Berzerk machine stopped making money, the arcade owner would spraypaint the thing, (usually black). Then they would toss in a conversion kit, to make that old cabinet into the latest game. Often this would happen several times in the life of a game. My own Mame Cabinet began life as a Pac-Man, (Namco cabinet serial number 25002), was then converted into an unknown game, then a Contra, and finally a Capcom Bowling.
An experienced arcade collector can often tell what a converted game used to be with only a glance. This is because most of the early games had a distinctive shape. The moment I first saw my own Double Dragon I knew that it used to be a Defender.
A game in a dedicated cabinet is usually worth at least twice what a game in a conversion cabinet is, (even more for some games). If you ever go to an arcade auction, you will see the dedicated games bring in big bucks.
The arcade industry is slowly returning to using dedicated cabinets again. But this is mostly a side effect of all the driving games that are being produced, (driving games are almost never converted). The golden age of painted dedicated cabinets is basically over.
As a final note. There are companies that make reproduction artwork for the most popular classic games. But the stickers they sell are not a true replacement for the hand painted cabinets of the early 80's. Plus they only make the reproduction stuff for extremely common games, (which are still fairly easy to find in good original condition).