Basically, say you are on a project with a co-worker of equal rank, neither of you wholly responsible for the work, but you are more commonly associated with the project.
In this situation, say your colleague makes an error. When this is discovered in a meeting or demonstration or brought to your attention. Assuming the colleague was present when it was discovered, which would be the more acceptable way of handling it?
You pointing out
"Ah, that was actually (person)'s contribution."
The colleague admitting:
"Oh that was actually my section, apologies."
You don't want to be automatically blamed for every mistake on a project you're associated with, but it also seems rude to be pointing the finger at your colleague, especially in front of others.