Crowded means there are more people in the space than it comfortably holds. A rush-hour train where nobody can reach a handrail, a beach in August, a bar where you shout to be heard.
Things crowd as well as people: a crowded shelf, a crowded diary, a crowded market where twelve firms sell the same thing. It is the past participle of crowd doing adjective work, which is why you also meet crowded out — pushed aside by everything else competing for room. Overcrowded is the stronger word and it carries a complaint: overcrowded prisons, overcrowded classrooms. An empty room is the opposite, and a deserted street is the vivid version of empty.
1adjectivecrowdedFull of people, with little room to move.
“The platform was so crowded that we let two trains go.”
synonyms: packed, jammed
2adjectiveholdingHolding too many things in too little space or time.
“My week is crowded with meetings I did not ask for.”
3adjectivemarketOf a market or field: full of rivals doing the same thing.
“It is a crowded market and nothing stands out.”
Too few real examples of this word to estimate which sense is commonest.
Also accepted in games: packed