clandestine, secret or furtive
The backstairs (stairs at the rear of a building).
Using unconventional, non-traditional, non-mainstream and often subversive practices to achieve something.
Relating to, using, or typical of guerrilla warfare, or its principles of small independent or non-official perpetrators.
Relating to, using, or typical of guerrilla marketing.
A soldier in a small independent group, fighting against the government or regular forces by surprise raids.