拥挤 (yōng jǐ) describes a place or space that is crowded with people or things, often to the point of discomfort. Unlike 人群 (rén qún), which is a noun meaning 'a crowd of people', 拥挤 is an adjective/verb focusing on the state of being packed. It is stronger and more negative than 挤 (jǐ), which can also mean 'to squeeze' or 'crowded' in a more neutral or action-oriented way.