Definitions for "ERDL"
Early leaf pattern camo, issued in Vietnam to recon, SF teams and Marines. Is somewhat similar to modern woodland but has different shades of green and brown, and came in highland (brown dominate) and lowland (green dominate) styles.
US Army "Engineer Research & Development Laboratories" - they developed the "leaf pattern" used by US forces during the Vietnam war
Engineer Research & Development Laboratory - developers of the 4 color camouflage. View Example.