Stroke is the line around text. It's a usual, simple technique to make text stand out or separate it from the background.
There is the layerfx plug-in, but I recommend Ofnuts' ofn-outline-layer.py
It's almost on top, here:
https://sourceforge.net/projects/gimp-tools/files/scripts/
Extract the zip archive and put the .py file in the Gimp user plug-ins folder.
You didn't mention your OS, in Windows (Gimp 2.10 series) that is:
C:/Users/"YourUserName"/AppData/Roaming/GIMP/2.10/plug-ins
In Linux:
/home/config/GIMP/2.10/plug-ins
Menu entry for the plug-in is Layer/Outline Layer Contents.
This is pretty simple plug-in, play with the settings and you'll soon find a pleasing result.
Note that it uses the active background color to stroke the path.
Just a quick example using Titillium font.