This article is about Block started by symbol (BSS), BSS can also mean Base Station Subsystem in GSM

Block Started by Symbol (BSS) was a pseudo-op in UA-SAP (United Aircraft Symbolic Assembly Program), the assembler developed in the mid-1950's for the IBM 704 by Roy Nutt, Walter Ramshaw, and others at United Aircraft Corporation. This pseudo-op was later incorporated into FAP (FORTRAN Assembly Program), the standard IBM assembler for the IBM 709, 7090 and 7094 computers. It defined its label and reserved space for a given number of words.

Most modern assemblers produce a BSS section in their output object module containing all reserved but uninitialized space.