From QB64.org wiki
The apostrophe is used to tell the compiler to ignore a statement or programmer comment.
- Allows programmer comments or temporary code removal.
- REM can also be used to "comment out" a line.
- QBasic metacommands must be commented either with an apostrophe or REM.
- $INCLUDE requires an apostrophe before and after the included file name.
COLOR 11: PRINT "Print this...." ' PRINT "Don't print this program comment!"