Never seen this before...just curious

I am trying to learn all aspects of coding, errors, definitions, and what means what

so i just refreshed IPS on the forums page, and for about 5 min's i got this

Quote

 

An error occurred (500 Error)

We're sorry, but a temporary technical error has occurred which means we cannot display this site right now. 

MySQL server has gone away

You can try again by clicking the button below, or try again later. 

 

lol i know nothing was wrong due to me typing this

but just for future reference (like when i eventually move to my own server) what "did" that mean?