A dialect is a subset of a particular language that generally presents regional differences in pronunciation, grammar characteristics, and vocabulary, yet remains mutually understandable between two native speakers. An "accent" is an even smaller group of the language that generally only involves pronunciation.
As an illustration, some dialects of English include: American English (as distinct from British English or Australian English at large), Appalachian English, Black English Vernacular, New York City Dialect (sometimes considered only an accent), Cajun English, Texan.
International dialects of English [1] National Map of Dialects of the United States [2] link showing dialects vs. accents [3]