Dialect 

A dialect  is a variety of language differing in vocabulary and grammar as well as pronunciation. Dialects are usually spoken by a group united by geography or class.

Accent 

When a standard language and pronunciation are defined by a group, an accent may be any pronunciation that deviates from that standard.

Groups sharing an identifiable accent may be defined by any of a wide variety of common traits.  An accent may be associated with the region in which its speakers reside (a geographical accent), the socio-economic status of its speakers, their ethnicity, their caste or social class, their first language (when the language in which the accent is heard is not their native language), and so on.