elliptical expression

An elliptical expression is a group of words with certain understood words omitted. Good writers routinely use elliptical expressions. You may punctuate elliptical expressions in two ways: (1) begin the expression with a semicolon, and then insert a comma where the omitted words would have appeared or (2) for simple expressions, insert a comma before the expression but omit the comma where the omitted words would have appeared.

Here are Mr. Strunk and Mr. White using an elliptical expression when discussing restrictive and nonrestrictive clauses. Notice that they opt for the simple punctuation:

That is the defining, or restrictive pronoun, which the nondefining, or nonrestrictive.

Here's an example using the semicolon technique:

Carolina has won three national titles; Duke, two.