A terziere (pl.: terzieri) is a subdivision of several towns in Italy. The word derives from terzo (lit. 'third') and is thus used only for towns divided into three neighborhoods. Terzieri are most commonly found in Umbria, for example in Trevi, Spello, Narni and Città della Pieve; towns divided into terzieri in other regions include Lucca in Tuscany, and Ancona and Macerata in the Marches. The medieval Lordship of Negroponte, on the island of Euboea, was also divided into three distinct rulerships, which were known as terzieri.

Other Italian towns with more than three official neighborhoods are frequently divided into analogous quartieri (4, whence the English word "quarter" to mean a neighborhood) or sestieri (6); some towns merely refer to these neighborhoods by the non-number-specific rioni. Terzieri, quartieri, sestieri, rioni, and their analogues are usually no longer administrative divisions of these towns, but historical and traditional communities, seen especially in towns' annual Palio.