Bitcoin: Can anyone tell me what is `ACK` and `utACK` means?

[micromaomao]

In some, or lots of, pull request, people say ACK, can anyone tell me what this meaning?

[fanquake]

See the notes in doc/developer-notes.md

Concept ACK - Agree with the idea and overall direction, but haven't reviewed the code changes or tested them.

utACK (untested ACK) - Reviewed and agree with the code changes but haven't actually tested them.

Tested ACK - Reviewed the code changes and have verified the functionality or bug fix.

ACK - A loose ACK can be confusing. It's best to avoid them unless it's a documentation/comment only change in which case there is nothing to test/verify; therefore the tested/untested distinction is not there.

NACK - Disagree with the code changes/concept. Should be accompanied by an explanation.

[micromaomao]

Thank!