真
zhēn
Expressing "really" with "zhen"
真 is the exclamation "really!" — a reaction, not a measured statement.
真 + Adj.
How it works
你女朋友真漂亮 is genuine admiration. Where 很 is structural filler, 真 actually means something.
Because it's a reaction, 真 belongs in exclamations rather than in neutral descriptions or comparisons. You wouldn't use it to answer a factual question about degree.
Examples
nǐ nǚ péng yǒu zhēn piào liang
你女朋友真漂亮。
Your girlfriend is really pretty.
jīn tiān zhēn rè!
今天真热！
It's really hot today!
zhè ge cài zhēn hǎo chī
这个菜真好吃。
This dish is really tasty.