(adj) beautiful; very attractive. It is a shortened form of saying outstandingly gorgeous that is often used to comment on instagram or facebook photos. It is the highest form of flattery. Originating in the suburbs of Philadelphia, the word "ga" is a hip, new word.
Related forms: "gallium," which is an element on the periodic table that has the chemical symbol of "Ga." Gallium also can be used to mean gorgeous.
person 1: OMG YOU LOOK GA IN THIS PICTURE!!!!
person 2: ILY BFF <33333