MAME stands for Multiple Arcade Machine Emulator. You can view the project and find out more details about it at the home page here:
I have only played around with MAME a little bit so I am not an expert on it. It can be very confusing as there are multiple versions and different ROM sets are qequired by different versions of the MAME emulator.
I found this article that explains about MAME Romsets very useful:
I will be adding to this page as I dig back into the MAME emulator both on PC and on the Raspberry PI as it is one of the emulators most compatible with light guns on Retropie and there are a lot of good games available. It does seem to require a fair bit of work to get going but looks worth it.
Here are a couple of guides that I have found usefull:
This is a great video that links to scripts to install and set up MAME on Retropie to work with the Aimtrak guns:
If you have any tips or guides on MAME, please post them in the comments to help everyone get set up and playing!