A language, used for expressing program designs, that is similar to a conventional high-level programming language but emphasizes structure and intention rather than the ability to execute programs expressed in the language. PDLs are often employed in conjunction with structured programming. When not executable they are termed pseudolanguages.

Typically the formal syntax of a PDL would cover data definition and overall program structure. Facilities in the latter area would include the basic control-flow constructs—sequential, conditional, and iterative—plus those for the definition and invocation of subroutines. These facilities would be used to define the overall framework of the program, but individual actions within the framework would be expressed using pseudolanguage—natural English mixed with a more formal semantically rich language. Correspondingly, the PDL facilities for data definition may be expected to be richer than those of a typical programming language, encompassing a broader range of basic types and a more extensive set of data-structuring facilities. A wide variety of PDLs have been defined; normal practice is to select one that is well-matched to the target programming language.