Okay kiddo, so imagine you have a teacher in your class who is really good at helping you and your friends learn new things. This teacher is called a "teaching fellow."
Basically, a teaching fellow is someone who helps other teachers in the classroom. They might work with the teacher to plan lessons or activities, or they might help students one-on-one if they need extra help.
Teaching fellows are usually college students or recent graduates who are studying to become teachers themselves. So, it's like they are practicing being a good teacher by working with another teacher!
They are kind of like a teacher-helper or a teacher-in-training. They get to learn a lot about teaching and helping students, while also helping the classroom teacher make sure all of the students are learning and having fun.