An electronic grade book is like a special computer program that helps teachers keep track of how well their students are doing in school. Imagine if the teacher had a magical notebook that could remember everything they have ever written down, but also did some math and organizing for them so they don't have to do it all by hand.
When a teacher puts a grade in this electronic grade book, it gets saved into the program. That means they can look back at all of the grades they have given to the whole class or to one student over time. It's kind of like a virtual report card!
The electronic grade book can also do some other cool things, like help calculate a student's average grade or show the teacher which kids need some extra help. It's a really useful tool for teachers to keep track of their students' progress and make sure they are doing well in school.