Different ways to organise information
An online shop might keep customers and orders in separate tables, with each order linked to a customer. That is common in a SQL database. SQL stands for Structured Query Language, used to read and change data in those tables. PostgreSQL (Postgres) and MySQL are examples.
NoSQL covers several other designs, including documents and key-value stores. MongoDB, for example, can keep a whole customer profile together in one document.
Choosing a fit
Both kinds can support large systems and set rules for their data. Teams choose based on how records relate and how the app needs to find or change them.