What does "on autopilot" mean?

Thanks for your question!

The literal meaning of autopilot is a device that steers a ship, plane, or spacecraft by itself, without a person. However, the expression “on autopilot” has developed a different meaning. Here are some typical uses of the expression “on autopilot,” which should make its meaning clear:

• He wasn’t thinking very hard, he just did his job on autopilot. 
• Instead of driving to school my brain was on autopilot, and I started driving to work!
• By the third week of her campaign for mayor, Quimby was making all of her speeches on autopilot.

As you can tell from the examples above, to do something on autopilot means to do it without focusing on it, without thinking about what is happening.

I hope this helps.