Hey @faraford! Welcome to the Spotify forums!
Scrobbling is a term used to describe the process of sending the songs you listen to, to a service, and that service keeps track of it and creates suggestions for you.
In other words, scrobbling is like building a live list of artists and songs that you may like based on your listening history.
Spotify uses the service Last.FM for this cool feature. Read HERE for more official information!
Hope this was helpful!