While much of the data in working with a database is stored on the disk and referred to via identifiers (e.g., table names, column names, and functions), there are obviously times when new data must be introduced to the system. This may be observed when inserting new records, when forming clauses to specify criteria to delete or modify, or even when performing calculations on existing records. This data is input through constants, which are sometimes called literals, because they literally represent a value in a SQL statement (rather than referencing an existing value by identifier).
An implicitly typed constant is one whose type is recognized automatically by PostgreSQL's parser merely by its syntax. PostgreSQL supports five types of implicitly typed constants:
Bit string constants
Floating point constants