What is Gapps fix?

Hi

i know it of course is a Google Apps Fix, but can't find any info about it on Google. Is it just the app in the play store Gapps fix?

What exactly do it do? Just disable some services and such? I just see more and more people are talking about it and some developers have added it to their roms and such.

Just heard it makes Android Wear stop working and such.

Thanks in advance