Loisaida ( /ˌloʊ.iːˈsaɪdə/) is a term derived from the Latino (and especially Nuyorican) pronunciation of "Lower East Side", a neighborhood in Manhattan, New York City. The term was originally coined by poet/activist Bittman "Bimbo" Rivas in his 1974 poem "Loisaida". Loisaida Avenue is now an alternative name for Avenue C in the Alphabet City neighborhood of New York City, whose population has largely been Hispanic (mainly Nuyorican) since the 1960s.

Today, there is much dispute over the borders of the Lower East Side, Alphabet City, and the East Village. Historically, Manhattan's Lower East Side stretched from the East River at the southern end to 14th Street at the northern end, bound on the east by the river and on the west by First Avenue. It originally comprised German, Jewish, Irish, and Italian working-class residents who lived in tenements, without running water; the German presence, already in decline, virtually ended after the General Slocum Disaster in 1904.

Note: Loíza (or Loíza Aldea) is a town in Puerto Rico; some people^[who?] believe that "Loisaida" comes from "Loíza Aldea".