1. <programming, compiler> Extra information associated with a particular point in a document or program. Annotations may be added either by a compiler or by the programmer. They are not usually essential to the correct function of the program but give hints to improve performance.
2. <hypertext> A new commentary node linked to an existing node. If readers, as well as authors, can annotate nodes, then they can immediately provide feedback if the information is misleading, out of date or plain wrong.