It is called bay (from Italian: corsia) to the architectural space between two load-bearing walls,[1]​ two alignments of pillars (porticos), or between a wall and the adjacent aligned pillars.

This space also refers to the naves "Nave (architecture)") or corridors of certain buildings, which give access to lateral rooms, as is the case of each of the galleries, or pandas, of a cloister. Constructively, it is each of the main parts into which the floor of a building is divided. The first bay is the one located closest to the façade, numbered consecutively towards the interior of the building.

The simplest architectural composition is the typology formed by the juxtaposition of bays. In this form of composition, the communication of the enclosures is established through the opening of holes in the walls; Gaps are also used to ventilate and illuminate the rooms. The partitioning of the bays is usually done using "Facing (architecture)" partitions.