stabs (sometimes written STABS) is a debugging data format for storing information about computer programs for use by symbolic and source-level debuggers. (The information is stored in symbol table entries; hence the name "stabs".) It "was apparently invented by Peter Kessler at the University of California, Berkeley" for use with a Pascal compiler.
When stabs was created in the 1980s, the dominant object file format was a.out, which (unlike more recent formats such as ELF) makes no provision for storing debugging information. Stabs works around this problem by encoding the information using special entries in the symbol table.
At one stage stabs was widely used on Unix systems, but the newer DWARF format has largely supplanted it.