There are so many words in the English language, the actual number can't even be provided. Some experts have tried to estimate, but there are new words being added all the time (and a ton of weird ones that people never really use). What I'm saying is, when you're writing about or writing with punctuation and letters, there's a word for that. There's a word for every itty bitty little piece of punctuation, for the extra add-ons in letters, for every wacky symbol you might find when you're reading.
Everything has a name, even in punctuation. Knowing the proper words for things comes in pretty handy, especially if you've got a question about proper usage. Trying to use a search engine without knowing the right words is an exercise in frustration...and won't you sound learned and impressive if you know that the little dot over the i and j is properly called a tittle?
It's a fun little word, a lot more interesting than the name for the little bar that crosses the t (which is simply known as a T-bar). We can thank the Germans for giving us umlauts, the double dots that sometimes appear over foreign words (like naïve).
The French love letter symbols. They gave us the circumflex, that little half-triangle over certain vowels, but you can find this mark in all sorts of languages. Depending on where and how it's being used, the circumflex represents stress on a vowel sound, a rising and falling tone and all sorts of other pronunciations.
Accent marks are those sweeping, slanted marks that appear over words like protégé. Sometimes, you'll find a weird mark underneath the letters. The funny little doodad hanging around on façade is called an ogonek, a Polish word that actually means little tail. You'll find funny n-words in Spanish with a curvy line over them (like piñata); that funny thing is called a tilde.
Put them all together, and what do you get? Diacritics. Sounds like a bunch of angry book reviewers, but that's the actual proper name for all those funny little letter extras that are used to denote specific pronunciation in words.
And once you know what they're called, you can actually use them. Digging through font and symbol sets in order to find the exact letter you need is such a tedious process, most writers don't bother (I don't). Many words that should have diacritic marks are written without them in American English, but technically that's not right. You can, however, keep a list of codes handy so you only have to type in a few numbers and make your correct marks. There's a word for everything. Once you know it, there's nothing you can't find out.