Shorthand for "Pure Grain Alcohol". This is a 95% pure ethanol (the other 5% is pure water which alcohol naturally bonds to, even when distilled). Sold under the brand name Everclear and many other small brands (nearly all of which are far less expensive than Everclear).
Being ethanol, it is nontoxic, and can be drank (though usually diluted) and is most frequently used around the home to either cook with/make extracts, or for cleaning.