The HLASM Language Reference does not use either term "pseudo operation" or "pseudo instruction." I must admit I was surprised! HLASM calls them "assembler instructions," and defines several types. Taken as a generic, a "pseudo operation," "pseudo instruction, or "assembler instruction" refers to Assembler code that appear to be a machine code but serve other purposes. Many Assemblers have a REM pseudo instruction to define a comment, but HLASM does not define such an animal in the manual.
- Program control - AINSERT, CNOP, COPY, END, EXITCTL, ICTL, ISEQ, LTORG, ORG, POP, PUNCH, PUSH, and REPRO.
- Listing control - CEJECT, EJECT, PRINT, SPACE and TITLE.
- Operation code definition - OPSYN
- Program section and linking - ALIAS, AMODE, CATTR, COM, CSECT, CXD, DSECT, DXD, ENTRY, EXTERN, LOCTR, RMODE, RSECT, START, WXTRN and XATTR.
- Base register - DROP and USING.
- Data Definition - CCW, CCW0, CCW1, DC and DS.
- Symbol definition - EQU.
- Associated data - ADATA.
- Assembler options - *PROCESS (Since *PROCESS starts in column 1, arguably it's not a pseudo instruction), ACONTROL.
I have to admit I've never used many of these; I'm just copying them from the HLASM Language Reference.