Okay kiddo, let me explain what British Rail railbuses are. Have you ever been on a smaller bus that can fit a few passengers, but is not as big as a regular bus? That's kind of what a railbus is, but it runs on train tracks instead of on the road.
In the 1950s and 1960s, British Rail, which is like a big train company in England, started using railbuses to provide transportation to smaller towns and villages. These places didn't have a lot of people who needed to get around, so it didn't make sense to run a big train with lots of seats. Instead, they used these smaller railbuses that could hold about 22 people.
The railbuses were different from regular trains because they didn't have a separate engine pulling them. Instead, they had their own engine underneath them, which is kind of like the heart of the train. The railbuses were also made with special wheels that could run on both train tracks and regular roads, so they could easily move from one type of path to the other.
Nowadays, British Rail railbuses are not as common as they used to be. The company has started using other types of trains and buses to transport people around, but the idea of a smaller, more efficient vehicle that can run on both roads and train tracks is still really cool!