The difference between 拥挤 and 挤
The adjectives 拥挤 and 挤 can have the same meaning of “crowded” in some contexts, but can also have different meanings in other contexts.
The similar meanings
The adjectives 拥挤 
and 挤 can be translated as "tight" and emphasize that there are many people or objects in a limited space.
and 挤 can be translated as "tight" and emphasize that there are many people or objects in a limited space.Examples
这么小的教室里放三十张桌子，太挤了
It is too tight to have 30 desks in such a small classroom
zhème xiǎo de jiàoshì lǐ fàng sān shí zhāng zhuōzi, tài jǐ le
今天路上该不那么拥挤了吧
The road should be less busy today, right?
jīntiān lùshang gāi bú nàme yōngjǐ le ba
那辆车坐了七个人是有点挤
This car is cramped with seven people
nà liàng chē zuò le qī ge rén shì yǒudiǎn jǐ
The other meaning of 挤
Sometimes the adjective 挤 may be used as a verb in the meaning of “to push against", "to squeeze”.
Examples
坐车的人太多了，我挤了半天才挤上车
There are too many people in the car. I had to squeeze in before I sat down
zuò chē de rén tài duō le, wǒ jǐ le bàntiān cái jǐshàng chē
他在人群中往前挤
He squeezed ahead in the crowd
tā zài rénqún zhōng wǎng qián jǐ
Other meanings of 拥挤
We can use the adjective 拥挤 in the meaning of “crowded”. It should be followed by the particle 的 .
. Pay attention
The adjective 挤 can’t be used with this meaning.
Examples
拥挤的市场是扒手大展身手的好地方
Crowded markets are a great place for pickpockets to show their skills
yōngjǐ de shìchǎng shì páshǒu dà zhǎn shēnshǒu de hǎo dìfāng
We also use 拥挤 as a verb in the meaning of “to crowd”.
Examples
请先下后上，不要拥挤
Please let people get off first before getting on. Do not crowd
qǐng xiān xià hòu shàng, bú yào yōngjǐ
乘客们拥挤在火车站上等候乘车
Passengers crowded at the train station while waiting to board the train
chéngkèmen yōngjǐ zài huǒchēzhàn shàng děnghòu chéng chē
Sometimes 拥挤 can be used as a noun for “congestion”, “crowd”.
Examples
交通拥挤是个大问题
Traffic congestion is a big problem
jiāotōng yōngjǐ shì ge dà wèntí
市场上的拥挤
There is a crowd in the market
shìchǎng shàng de yōngjǐ