What is pseudo-op in assembly programming?

Question

What is pseudo-op in assembly programming?

I read a statement at this page:

"If a particular symbol appears in the source code, but is not found in the symbol table, then the symbol was never defined. That is, the assembler did not encounter the symbol in the label field of any of the statements scanned during the first pass, or the symbol was never the subject of a .comm, .csect, .lcomm, .sect, or .set pseudo-op."

Answer 1

Pseudo op stands for "pseudo operation" and is sometimes called "assembler directive". These are keywords which do not directly translate to a machine instruction. Examples are the ones mentioned in your questions or .data, .def, .desc, .dim, .double, .eject, .else, .elseif, .end and many more. Refer to your assembler manual.