To mispronounce is to say something incorrectly. It can be pretty awkward when you mispronounce someone's name, especially if you know the person well.
Some words are easy to mispronounce, like February, realtor, and meteorology, simply because the sounds don't flow gracefully off the tongue. In other cases, non-native English speakers might mispronounce a word because it doesn't sound at all the way it looks — like tongue, for example. In any case, the verb mispronounce combines the prefix mis-, "wrong or bad," and pronounce, "to utter or say."