seseo

Seseo is a phonological feature of Spanish in which the sounds written as s, z, and the c before e or i are pronounced as a single sibilant, typically [s]. In seseo dialects there is no distinction between the sibilants that spell s and those that spell z or c before e/i; all are pronounced the same. This contrasts with distinción, a system in which s is pronounced [s] and z/c before e/i is pronounced [θ], and with ceceo, where s as well as z/c before e/i are realized as [θ].

Geographic distribution and variation: Seseo is widespread in the Spanish-speaking world. It is the standard pattern in nearly all of Latin America and is common in the Caribbean and parts of the southern and Canary Islands dialects in Spain. In much of mainland Spain outside these areas, distinción remains common, with ceceo occurring in some southern localities. The presence of seseo is a major phonological difference that can align with other regional traits, such as yeísmo.

Relation to other features: Seseo often coexists with yeísmo, the broad tendency to merge the sounds represented by ll and y into a single sound. It is a stable regional feature that affects pronunciation and perception but does not by itself convey a specific national or social background. In sociolinguistic studies, seseo is frequently discussed alongside other variation patterns to map Spanish dialect geography.