Simply put, marking online text to indicate sarcasm. Even verbally, sarcasm doesn't always carry over well. Some people just can't recognize it. Some people just can't express it. On the Internet it's worse. While it's bad to act out an emotion by merely stating that you feel that way, on the Internet it is sometimes necessary to indicate emotions such as sarcasm. Here is one way to mark it up: Scare Quotes or Tradesnark may also be regarded as examples of this. Ditto for using capitalization to mock-assert that some type of Serious Business is being discussed.