HLASM is IBM's high-level assembler product for its z/OS, z/VSE, z/VM and z/TPF operating systems, which run on its z/Architecture mainframe computers. There is also a version that runs on Linux, primarily intended for systems running on a z/Architecture system (this environment is sometimes referred to as z/Linux).
Based on IBM's H assembler, it allows assembly programmers to write code that uses some features normally associated with high level languages. Some of these features include labeled and dependent USINGs, more complete cross-reference information, and additional macro language capabilities such as the ability to write user-defined functions.
For a brief description of the language, see IBM Basic assembly language.