The Atari 8-bit computer range is a family of home computers made by Atari between 1979 to 1992. While the machines did okay in the US and the UK in terms of support but not as huge as competing systems, they were more successful in Eastern European countries such as Poland. Since most models only differentiate in terms of model design, color palette changes, memory and production costs, it is considered confusing with the model names including different countries where they have different name for the computer so this name was unofficially adapted.
While the Atari 5200 is based off the Atari 8-bit computer range in terms of hardware, it is not compatible with it. There is a console version of the Atari 8-bit range though called the Atari XEGS that is directly compatible with the 8-bit cartridges and accessories but not the 5200 ones. There are even a few "console exclusive" versions of the games such as Mario Bros. and Barnyard Blaster.
Done by the same developer as the VirtualDub software, Altirra is a very accurate Atari 8-bit emulator that also supports 5200 games. The downsides are that it is not easy to set up and it is Windows only.
kat5200 is an Atari 5200 emulator that is easier to set up and also supports some of the Atari 8-bit range as well, mainly the 400/800 models.