What does it mean to grow a bump under your tongue?

Many Possibilities: There are several different causes of bumps under the tongue, as you can image. The most common is called a "mucocele." this can be a cyst, a ruptured or blocked salivary gland, an infection, and so on. You really need to see a dentist or oral surgeon to know for sure...Especially if it doesn't resolve on its own within a few days.