What is the definition of layer in auto cad?

Answer 1

Layers can be used to combine or separate objects in a plan.

For example, if you were using AutoCAD to draw a map, you might have one layer to define water, another for roads, another for buildings, and so on. Then if the waterline changed for some reason, you would only need to go to the Water layer and make the required changes. Viewing the other layers would tell you if the change in the Water layer would affect the Roads or the Buildings.