a schema is the organization or structure for a database. The activity of data modeling leads to a schema.
A database schema of a database system is its structure described in a formal language supported by the database management system and refers to the organization of data as a blueprint of how a database is constructed. The formal definition of database schema is a set of formulas called integrity constraints imposed on a database. These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language. A database can be considered a structure in realization of the database language. The states of a created conceptual schema are transformed into an explicit mapping, the database schema. This describes how real world entities are modeled in the database.