Engineering education research means that people study how we can teach engineering in the best way possible. Just like your teacher helps you learn math or reading, some people study how to help students learn to be engineers.
They look at things like how people learn best, what teaching methods work well, and how to design classes that help students understand engineering concepts. They might also study how to make engineering more interesting or fun for students, so that they want to learn more.
By doing all of this research, they hope to make engineering education better for everyone, so that more people can become engineers and help create new things to make the world a better place.