Databases
A database is an organized collection of data. It is the collection of schemas, tables, queries, reports, views, and other objects. https://en.wikipedia.org/wiki/Database
A very basic and nice explanation of the types of DBMS: https://www.youtube.com/watch?v=FR4QIeZaPeM&feature=emb_logo
NoSQL databases:
This is good to start understanding NoSQL databases and the difference with relational databases: https://www.youtube.com/watch?v=uD3p_rZPBUQ
Data Warehouse:
This is a very good explanation of what a Data Warehouse is: https://www.youtube.com/watch?v=k4tK2ttdSDg