Badass, awesome, seriously impressive.
The highest-energy compliment in casual Mandarin. 太牛逼了 means "that is incredible." Softened to just 牛 (niú) in mixed company, and written NB online to dodge the vulgarity.
Literally "cow" plus a crude anatomical word. The polite written form is 牛 or NB.
The full form is genuinely crude. Use 牛 or 厉害 (lìhai) with anyone you are not close to.
Reading a definition isn't the same as saying it to someone. Lingo Kaiava is a voice tutor set to Chinese — it uses 牛逼 the way locals do, corrects you in the moment, and never "fixes" the way real people actually talk into textbook Chinese.
Free to start. No signup for your first conversation.