What does "GDS" mean?

The only reason I'm going through a travel agent is I found a cheap fare. They're holding a $1200 ticket from SJC-SIN over the xmas and new years holidays. There was only one seat left on the departure date 12/21 (i'm still rather confused about how the fare codes and fare buckets work) at that cheap rate.

I never use travel agents becauase I'm usually booking my trips thru the internet. However in this case I'm unable to hold a multi-carrier reservation except thru a travel agent. Anyways, I'll go talk to the travel agent and see what he says ... I'll report back later! (can you tell I'm avoiding the agent?)