To surmount something. During World War I this term signified climbing over the parapet of front-line trenches to attack the enemy, and by extension this came to mean doing something dangerous or notable. After World War II the phrase took on the additional meaning of going above and beyond what had been originally planned, as in, “Her generous donation put us over the top; we’ve exceeded our goals.” And finally, in the later 1900s, the phrase took on yet another meaning, to go too far or beyond reasonable limits, as in, “Making the entire chorus wear flesh-colored body suits—that’s going over the top.” With all these usages one must rely on the context to figure out which sense is meant.