PokerTracker

Sorry, I've googled it but don't understand the definition very well. Can someone tell me

1. What is it and the purpose of it?

2.How does it relate to Poker Tracker 3?

3.Is there anything I should know about it? Can it harm the PC potentially? More susceptible to viruses? Tax the CPU or RAM? Etc...

Postgres is the database service that PT3 uses to store the hand histories and statistic information.
You need to have it installed.

WhiteRider wrote:Postgres is the database service that PT3 uses to store the hand histories and statistic information.
You need to have it installed.

Why wouldn't Poker Tracker store this information on the user's own computer? What benefit does it serve to have it everyone's centralized?

It does store it on your local computer - your information is not shared with anyone; this is against all sites terms and conditions.