In a nutshell, a cloud database is many computers connected and communicating in real-time using the internet. It is the same as a traditional database but with the flexibility to be accessible anywhere. Storage is scalable to what is needed as a cloud database is not limited like a traditional database.
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If you wanna know more you can read this book for a better understanding: https://www.amazon.com/dp/B08C6THB8T
My friend works for a company that provides cloud implementation and summarized their beginner understanding in this book. I'm sure you will learn alot from there as the project was also deciding between using AWS or Azure and there is an explanation on why they chose it.
Here's the book. Its good for beginners :) https://www.amazon.com/dp/B08C6THB8T