Extremely long-serving American camouflage pattern used by all branches of the American military from 1981 until the early-mid 2000s, though it remains in service with some units, in particular American special forces who choose it over more modern pattern. M81 Woodland is an enlarged printing of the ERDL pattern, which was used in limited numbers during the Vietnam War.
The pattern has been used by all American allies, exported to a tremendous number of countries, copied by numerous militaries including the Soviet Union and modern-day Russia. It has become so ubiquitous and recognizable it is the camouflage nearly all "generic" camouflaged is based off. If you know it's camouflage but don't know what the name is, it might be this. It has also become a staple of fashion design.
The pattern consists of high contrast splotches of green, a light off-lime green, brown and black.