What is Schema and instances?

In DBMS,Schema is the overall Design of the Database.Instance is the information stored in the Database at a particular moment.In programming,you declare a variable which corresponds to "Schema".But its values changes as and when required which corresponds to "Instance".
Google about levels of Database Abstraction.

Physical Schema describes database design at physical level while a logical schema describes the database design at the logical level.A database may also have several schemas at the view level, sometimes called subschemas, that describe different views of the database.