Okay kiddo, End User Development is when regular people who don't know how to code or develop software, make their own programs and tools using simple software tools. Think of it like building something with blocks or Legos, but instead of blocks, people use software tools to make their own tools and programs.
Using these tools, normal people can create scripts, macros, spreadsheets, databases, and even simple websites, without having to be programmers or computer experts. It's kind of like cooking dinner, where you use simple ingredients to make a tasty meal, except instead of food, you're using simple software tools to create amazing things.
End User Development is really popular these days because it empowers people who don't have access to advanced software tools or programming languages to still be able to create their own software and tools, which can be really helpful for all sorts of things from organizing their finances, to making their work more efficient, to sharing information with their friends and family. So, that's End User Development in a nutshell!