Class is an object-oriented programming term for a method of defining sets of related objects that share certain characteristics. In HTML, the class attribute (CLASS=...) defines subclasses of elements.
The attribute CLASS=... can be used with a broad variety of elements to create subclass tags. The DIV element, <DIV CLASS=APPENDIX>, for instance, defines a division that acts as an appendix. <H2 CLASS=Section> defines a level 2 header that acts as a section header. <P CLASS=STANZA.COUPLET> defines a paragraph that acts as a couplet in a stanza.
By convention, the class names are interpreted hierarchically, with the most general class on the left and the most specific on the right, with classes separated by a period.
CLASS was introduced in HTML version 3.