There are two meta tags that seem very similar: description and abstract. What is the difference between the two?
It depends on the definition of
abstract is not registered. So you must not use this metadata name in (X)HTML5 documents. The metadata name
description is defined in the HTML5 specification itself, so it’s valid to use it in (X)HTML5 documents.
This specification does not define a set of legal meta data properties. The meaning of a property and the set of legal values for that property should be defined in a reference lexicon called a profile.
Metadata can only be useful if it’s use/scope is defined (e.g. in specifications) resp. documented (e.g. by metadata consumers).