Bind Variables & Host Variables

Bind variables are used in SQL and PL/SQL statements for holding data or result sets. They are commonly used in SQL statements to optimize statement performance. A statement with a bind variable may be re-executed multiple times without needing to be re-parsed. Their values can be set and referenced in PL/SQL blocks. They can be referenced in SQL statements e.g. SELECT. Except in the VARIABLE and PRINT commands, bind variable references should be prefixed with a colon.
Host variables are the key to communication between your host program and Oracle. Typically, a pre-compiler program inputs data from a host variable to Oracle, and Oracle outputs data to a host variable in the program. Oracle stores input data in database columns, and stores output data in program host variables.
A host variable can be any arbitrary C expression that resolves to a scalar type. But, a host variable must also be an lvalue. Host arrays of most host variables are also supported.