Plain English Meaning
A short, simple set of seven flashing lights that lead the pilot's eye toward the runway during an approach. Five flash in sequence along the centerline ahead of the runway, and two more sit on either side of the runway's beginning.
Full Definition
A simplified approach lighting system consisting of seven omnidirectional flashing lights: five lights spaced at 300-foot intervals along the extended runway centerline outward from the runway threshold, and two lights placed one on each side of the runway threshold. The lights flash in sequence from the outermost light toward the threshold to guide the pilot's eyes inbound to the landing runway. ODALS is typically installed at non-precision instrument runways at smaller airports.