For future reference, if you click through from the tag page listing questions via "Learn more..." you will find an additional page of just information, who's URL has an
All three of those (now) have a link to an official homepage which makes fairly clear the difference between them. In addition I've added this to each:
If you are not aware, there are a number of different pieces of software that serve a similar fundamental purpose (controlling the Raspberry Pi GPIO pins) and are independent of one another. Not surprisingly, they also all use spins on combining "rpi" and "gpio" in their name. Each has a separate tag and questions about their use should use that specific tag. This is documented here to prevent confusion.
pigpio library, written in C but with ports to python and other languages: Tag pigpio
RPi.GPIO module for python: Tag rpi.gpio
This isn't intented as an exhaustive list of such software, just the three most prone to confusion here due to the similar names perhaps made more similiar by restrictions on tag labels (all lower case, etc).
But with the list re-arranged to put the current on on top annotated, "The page you are on now is for...".