The HP 48 is a series of graphing calculators designed and produced by Hewlett-Packard from 1990 until 2003.

The models with an X suffix are expandable via special RAM (memory expansion) and ROM (software application) cards.

The calculators use Reverse Polish Notation (RPN) and the RPL programming language.

The HP 48 series of calculators support a stack-based programming language named RPL, a supposed combination of Reverse Polish notation (RPN) and Lisp.

System RPL requires an external compiler; this may be done on the calculator with a third-party utility, or on another machine.

The two languages vary mainly in the number of low-level operations available to them.