Umlaut definition

I heard the word umlaut the other day & thought "Hmm that's a funny word. I don't know what it means, but I wish I did because I bet it's a lot of fun to say". For some reason I thought an umlaut was a combination of shorts & a skirt. I still don't know what those are called. Apparently, an umlaut is a form of punctuation, the kind that you'd need reading magnifiers to identify. Dictionary.com defines umlaut as:

a mark (¨) used as a diacritic over a vowel, as ä, ö, ü, to indicate a vowel sound different from that of the letter without the diacritic, esp. as so used in German.

Now I know. I just have to be able to work it into a sentence now.