Depends on the database server.
MySQL doesn’t care, its basically the same thing.
In MySQL, physically, a schema is synonymous with a database. You can substitute the keyword
SCHEMA instead of
DATABASE in MySQL SQL syntax, for example using
CREATE SCHEMA instead of
Some other database products draw a distinction. For example, in the Oracle Database product, a schema represents only a part of a database: the tables and other objects owned by a single user.
DB2, and other enterprise level database solutions make a distinction.
Usually a schema is a collection of tables and a Database is a collection of schemas.