What is a DD statement? Keep seeing //something DD

COBOL has SELECT ... ASSIGN TO INFILE. JCL has //INFILE DD DSN=...

Is the DD just how you point the program at a real dataset?

Yes. DD = data definition. The name after // must match what the program expects (ASSIGN TO name, or SORTIN, etc).

DSN= says which dataset. SYSOUT=* means print to the spool. Dummy / DUMMY means no real file.

So if ASSIGN TO CUSTIN I need //CUSTIN DD ... Got it.