What is the difference between the description and abstract meta tags?

Question

There are two meta tags that seem very similar: description and abstract. What is the difference between the two?

Solution 1

It depends on the definition of abstract.

For HTML5, 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.

In HTML 4.01, you can use any metadata names, so using abstract would be allowed. But it should be defined in a profile:

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).

Solution 2

Another answer could be which meta tags are recognised by search engines. For example, abstract is not understood by Google as a valid meta tag whereas description is. Other search engines may have different criteria.