History of UML

metamodel

A metamodel is at a higher level of abstraction than a model. It is often called “a model of a model“. It provides the rules/grammar for the modelling language (ML) itself. The ML consists of instances of concepts in the metamodel
A metamodel describes the rules and constraints of metatypes and metarelationships
Concrete metatypes are instantiated for use in regular modelling work.

In object-oriented programming, a metaclass is a class whose instances are classes. Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances.

Modeling language

A modeling language is any artificial language that can be used to express information or knowledge or systems in a structure that is defined by a consistent set of rules. The rules are used for interpretation of the meaning of components in the structure
The more mature modeling languages are precise, consistent and executable. Informal diagramming techniques applied with drawing tools are expected to produce useful pictorial representations of system requirements, structures and behaviors, but not much else. Executable modeling languages applied with proper tool support, however, are expected to automate system verification, validation, simulation and code generation from the same representations

Glossary of Unified Modeling Language terms

Glossary