This is surely a basic question, but I have no idea about guitars.
Take the following song as an example:
At the 7 second mark, but more prominently between 8 and 9 seconds (and many other times) you can hear some kind of "transitioning" screechy sounds.
Does this have a name? Is it intentional and part of the music or an undesirable byproduct? It seems to give some "texture" to the sound, but I have no idea. I do hear it often in many songs though.