QBASIC is a simple BASIC programming language introduced in the 1980s. It has a direct mode for executing single commands and a program mode for writing and running programs with line numbers. QBASIC programs use commands like PRINT, LET, REM, CLS, and END. Variables can be numeric or alphanumeric, and constants can be numeric or strings enclosed in quotes. Programs are made up of statements executed in order, following syntax rules.