Final answer:
ACU stands for Army Combat Uniform, it's the combat uniform of the US Army. The authorized camouflage patterns have included the Universal Camouflage Pattern (UCP) and now predominantly the Operational Camouflage Pattern (OCP).
Step-by-step explanation:
ACU stands for Army Combat Uniform. It is the standard uniform worn by the United States Army personnel for combat. Over the years, the patterns have evolved to meet the changing environmental and tactical needs. The different camouflage patterns authorized for wear include the Universal Camouflage Pattern (UCP), used from 2005 until it was discontinued in 2019, the Operational Camouflage Pattern (OCP), which originated with the Multicam pattern, and is currently the standard camouflage pattern after fully replacing UCP, and the Operational Camouflage Pattern (OCP), which began replacing the UCP in 2015 and has become the standard issue since 2019. Each pattern is designed to blend into specific environments to provide soldiers with concealment on the battlefield.