The title of the poem is just the first line: "Break, break, break." In the context of the poem, it's the speaker telling the sea waves to "break, break, break" against the rocks. But lots of other things break, too, right? Like mirrors, or glasses, or hopes…or hearts. You get the picture: it's not a happy word, generally speaking.
The repetition in the title is important. The first line (and the title) emphasizes that the ocean waves are going to keep breaking, and breaking, and breaking, no matter what the speaker does. Time continues to pass, even in the wake of great tragedy.