A Lighting Pass isolates the contribution of a light source. Each light pass behaves as if all the other lights in the scene are switched off. The individual light passes can be added together to recreate the original render in post or to further adjust the individual contributions of each light during post.
Using lighting passes is easy. For example, the following scene has 2 lights and one Octane Daylight. Each of the emission lights has a "Light Pass ID". If you activate the corresponding IDs in the Render Pass settings, you can see the result in Live Viewer. In addition to Emission Lights, you can also render "Ambient" and "Sunlight" passes. Ambient light captures ambient light in either a daylight environment or from a texture environment. Sunlight captures the light of the sun. Only useful when a daylight environment is configured. When compositing, all these passes will be quite useful.