From W3C Wiki
The <s> element represents contents that are no longer accurate or no longer relevant.
- The s element mark a span of text as having been removed from a document. when indicating document edits, use the del element.
See global attributes.
In this example a recommended retail price has been marked as no longer relevant as the product in question has a new sale price [try it]:
<p>Buy our Iced Tea and Lemonade!</p> <p><s>Recommended retail price: $3.99 per bottle</s></p> <p><strong>Now selling for just $2.99 a bottle!</strong></p>
The HTML5 specification defines the <s> element in 4.6.5 The s element.