Casual interjection or adjectival noun used to express approval, satisfaction, or that something is good. Often used in informal conversation, similar to English 'good' or 'nice'.
from English good
This ramen's flavor is really great.
This idea is good, isn't it?
The test result was good.
Good! Keep it up.
「テストどうだった？」「グー！」
"How was the test?" "Great!"
fist bump
just right!; excellent!; perfect!
Loanword from English 'good', adapted into Japanese as グー. The long vowel is represented by the prolonged sound mark (ー).