Plain English Meaning
An LDA is a runway approach guidance signal that works like a localizer but points slightly off to the side of the runway instead of straight down it. Pilots use it to get close to the airport on instruments, then line up with the runway visually for landing.
Full Definition
A Localizer-type Directional Aid is an instrument approach navigation facility comparable in accuracy to a localizer but not aligned with the runway centerline. Course alignment offsets greater than 3 degrees prevent it from being designated as a localizer-based approach, and straight-in minimums may or may not be published depending on the alignment and descent angle.
Context Anchor
Seen on instrument approach charts and in planning when deciding whether an airport has a usable instrument approach.