At what point does search quality degrade to the point where is becomes a bug?

A bug is when actual behavior does not match stated or intended behavior. If the search bears little connection to what was searched for, then it is a bug, as far as the user is concerned.

Or maybe you mean to say we should reserve the word bug for deviations that are unintentional?

For me the idea that poor quality search results are a bug muddies the idea of what a bug is. It's like saying the colour of the paint in my living room is buggy because I don't like it. It might be an ugly colour that I don't like, but it is what it is. A bug would be if the colour doesn't match what was shown on the tin.

> If the search bears little connection to what was searched for, then it is a bug, as far as the user is concerned.

A bad product perhaps, but not a bug.

The trouble is, there are three different "versions" of "the search didn't work," only one of which I would say is definitely a bug:

- The thing the user searched for doesn't exist, so it wasn't found. This is not a bug.

- The user did a good job of searching, using relevant keywords etc, but the relevant thing (which exists) didn't come up. This is a bug.

- "Search didn't read my mind" -- if search is a core competency this is a bug, but otherwise I would consider it a deficiency or a missing feature.