Wiktionary
n. (context computing English) The default operational mode of x86-compatible CPUs, offering direct software access to all memory and peripherals but without the advanced features of protected mode.
Wikipedia
Real mode, also called real address mode, is an operating mode of all x86-compatible CPUs. Real mode is characterized by a 20- bit segmented memory address space (giving exactly 1 MiB of addressable memory) and unlimited direct software access to all addressable memory, I/O addresses and peripheral hardware. Real mode provides no support for memory protection, multitasking, or code privilege levels. Before the release of the 80286, which introduced protected mode, real mode was the only available mode for x86 CPUs. In the interests of backwards compatibility, all x86 CPUs start in real mode when reset, though it is possible to emulate real mode on other systems when starting on other modes.
Usage examples of "real mode".
Mr Pickering had heard somewhere or read somewhere--he rather thought that it was in those interesting but disturbing chronicles of Raffles--that the first thing an intelligent burglar did was to assume some open and innocent occupation to avert possible inquiry into his real mode of life.
His real mode has always been something dreamier, crazier, more didactic, nearer to Mark Twain than to Fred Pohl.