West Germanic is the largest branch of the Germanic family of languages, including such languages as English, Dutch, and German.
The other families of Germanic are North Germanic and East Germanic.
History
There was never a West Germanic proto-language from which all the languages currently in the group seem to have derived. As such the grouping is more of a geographical convenience to categorize languages that share many similarities with each other but also individually compare closely to particular aspects of North Germanic or East Germanic.
Family tree
Note that divisions between subfamilies of Germanic are rarely precisely defined; most form dialect continua, with adjacent dialects being mutually intelligible and more separated ones not.
See also