Since the question is tagged as biblatex, I answer with some quotes from the biblatex documentation (which you can get from here).
Regular Types
proceedings
A single-volume conference proceedings. This type is very similar to @collection.
It supports an optional organization field which holds the sponsoring institution.
The editor is omissible in terms of ยง 2.3.2.
Required fields: title, year/date
inproceedings
An article in a conference proceedings. This type is similar to @incollection. It
supports an optional organization field.
Required fields: author, title, booktitle, year/date
Type Aliases
conference
A legacy alias for @inproceedings.
To summarize:
proceedings is intended for a collection of articles, typically the written-up contributions of one conference. You use proceedings when you want to refer to the collection at large, and not to a single article. A proceedings reference thus typically has an editor specified rather than an author.
inproceedings on the other hand refers to a single article or contribution within a collection, i.e. typically a single written-up conference talk. You use it to refer to this specific contribution, and thus typically specifiy an author.
conference is only kept for compatibility reasons, use inproceedings instead.