The phrase "well attended" typically means a significant number of people attended an event or gathering. Synonyms for this phrase could include "heavily attended," "crowded," "packed," "busy," "well-populated," "well-attended," or "thriving." Other alternatives could be "jam-packed," "well-supported," or "well-attended." These words can be used to describe a wide variety of events, including concerts, sporting events, festivals, trade shows, and conferences. Ultimately, the use of synonyms can help writers add variety to their descriptions and convey the level of success and popularity of a particular event or gathering.