Since doncherry has added his suggestion as an answer, I'll expand a bit on my comment.
I don't think "initial" is a good candidate for a tag name. Even if the term is the more correct one, if it doesn't resonate with (average) questioners, then it either won't get used or will get used for other purposes. "initial" to (most?) English speakers has really only one salient meaning: words/names shortened to their initial letters. Now granted, drop-cap is also fairly technical, but it is used in other software that people might have experience with, e.g. Microsoft Word and Adobe InDesign, and therefore I think the "drop-cap" version is to be preferred (German speakers notwithstanding. :-).)
The Wikipedia version makes sense, a drop cap is an initial that extends into the line(s) below, but an initial might as well extend into the space above.
To the Germans among us, initial might be more telling than drop-cap since the German word is Initiale.
The understanding issue Alan mentioned is interesting. The only question that actually refers to this kind of letter is asked by an Austrian, the others don't use technical terminology.
Since there aren't too many questions (= 3) about these matters on here, a distinction between general initials and drop caps doesn't seem appropriate, but neither does tagging a question about an initial with "drop-caps". Hence, I think renaming the tag is a good idea.
Maybe the name could be initial-something where something is something appropriate (not being an expert, I have no idea what the "something" could be). I wouldn't realise what initial was and that a "drop cap" was an example thereof. Whilst "drop-cap" and "initial" may be both technical terms, "drop-cap" is fairly unambiguous (I guess one could take it to mean "lowercase" if one were being very obtuse) but (as has been pointed out) "initial" is not.