Stories We Like: A Guide to the Comma
late 15c., from Middle French paragraphe "division of text" (13c., Old French paragrafe), from Medieval Latin paragraphus "sign for start of a new section of discourse" (the sign looked something like a stylized letter -P-), from Greek paragraphos "short stroke in the margin marking a break in sense," also "a passage so marked," literally "anything written beside," from paragraphein "write by the side," from para- "beside" (see para- (1)) + graphein "to write" (see -graphy).
A basic unit of prose. It is usually composed of several sentences that together develop one central idea. The main sentence in a paragraph is called the topic sentence.