TSR is the acronym given to a now defunct hobby site known as TroothSayeR. It was based out of OC California

TroothSayer recently was reborn being hosted by a bunch on the east coast (but still is heavily comprised of OC and Inland Empire west coast hobbyists). It is now called TroothSayerZ. What acronym/abbreviation they're giving to this new iteration I do not know.

...showing my old geeking DOS knowledge off...

TSR is Terminate and Stay Resident.  It was used in the old DOS (before Windows) days to make a program stay in memory to be able to perform some function.   This might include keyboard enhancements, a network driver, or a popup program to allow some small functionality to happen.

In the old days, you might have 5 or 10 TSR in your system to load different functionality.   They all took up precious memory, resulting in a very slow computer (kind of like the viruses we have now).