lane
A narrow path or marked strip for travel or activity.
A lane is a narrow path or strip designated for a specific purpose. On roads, lanes are the marked sections that keep traffic organized: cars stay in their lane while driving, and drivers signal before changing lanes to merge into the flow beside them. Highway lanes help prevent accidents by giving each vehicle its own space.
In swimming pools, lanes are the sections marked by floating rope dividers. Each swimmer stays in their lane during races so they don't interfere with competitors. Track runners also race in lanes, marked by painted lines on the ground.
The word appears in many useful expressions. When someone tells you to stay in your lane, they mean you should focus on what you know or what's your responsibility, not interfere in areas that aren't your concern. If you're working on a group project and someone who's supposed to be illustrating the poster keeps trying to rewrite everyone's text, you might remind them to stay in their lane.
Small country roads are sometimes called lanes, especially in Britain and rural America. These peaceful country lanes wind through farms and forests, sometimes barely wide enough for two cars to pass.