Sounds like he was being a little picky (a LOT, actually) but he might have been looking for something like this...
Joins indicate how the server should use data from one table to select the rows in another table.
A join condition defines the way two tables are related in a query.
The oh-so-subtle difference is that in your definition, you stipulated they were to "retrieve data"... not necessarily true... joins could be used "in a query" just to identify which rows of a table should be updated with a constant (for example). Not all "queries" are SELECTs...
Like I said, though... whoever the interviewer was, he was being really picky... I'd have been tempted to ask him what 2 to the zero power is or what 14 base 16 in decimal is just to get revenge on being so picky :D
Consider this... if he's going to be THAT picky, you probably didn't want to work there, anyway... guy sounds like a jerk.