REM
REMark
REM is a BASIC language instruction — short for REMark — that marks a line as a comment in the source code. The interpreter skips the entire line without executing anything: no output, no computation, no side effects. Its sole purpose is to communicate intent to whoever reads the listing.
How it works #
When the BASIC interpreter encounters REM, it advances to the next line number and continues execution from there. In most dialects (Commodore BASIC, GW-BASIC, QBasic), a line number precedes the instruction:
10 REM VAT calculation program
20 LET RATE = 0.22
30 REM Enter the net price
40 INPUT PRICE
50 LET VAT = PRICE * RATE
60 PRINT "VAT: "; VAT
Several dialects also accept a shorthand apostrophe (') as a synonym for REM, behaving identically at runtime.
When it matters #
REM was often the only mechanism available to leave a human-readable explanation inside a program at a time when IDEs, diff tools, and version control systems did not exist. A listing without REM statements could become opaque even to its original author within weeks.
Today REM is primarily a historical and cultural reference: it marks the origin of inline code documentation, a practice that evolved in modern languages into docstrings, annotations, and structured comment formats.