Angela Delveccio was a girlfriend of Joey's. Joey dated her in the period just prior to the show's timeline.
Joey runs into Angela at Central Perk, where she reveals herself to be dating a man named Bob. Joey proposes that he and Monica go on a double date, intending to break up Angela and Bob and take Angela for himself.
Throughout the series, Angela Delveccio is mentioned three times. Chandler tells Joey that their kitchen table was fine until his "little breakfast adventure" with her. A few years later Chandler asks Joey what he gave Angela for birthday presents. Joey responds that she didn't have a birthday while they were going out, to which Chandler replies "For three years?!". This proves that they had a long-term relationship.
Though it's not officially stated that Angela Delveccio is the same one we see onscreen in "The One With The East German Laundry Detergent", there's no evidence that it's not her. Even though Joey dates a lot of women, it seems highly unlikely that he would have two ex-girlfriends named Angela within the span of a few months.
At the end of "The One With The East German Laundry Detergent", Joey and Angela get back together, but probably split up soon after that again, since she's never seen anymore.