Okay kiddo, so you know how some people have houses that they live in and some people have houses that they rent out to other people?
Well, buy to let is when someone buys a house specifically with the intention of renting it out to other people. They're called a landlord!
The idea is that the landlord will buy a house, maybe fix it up to make it nice for renters, and then find people who want to live there and charge them rent money.
The landlord has to be careful when they choose tenants though. They want to pick someone who will pay their rent on time and take care of the house.
The landlord can make money through buy to let because they charge rent every month and hopefully make more money than they spend on the mortgage, repairs, and other things related to the house.
It's important to remember though, that being a landlord can be a lot of work and requires responsibility to take care of the people who live in the house.