BaaS
Backend as a service: a database, logins, file storage and server code that are already running, so you only build the app on top.
Also called backend as a service.
Every app has a front and a back. The front is what people see and tap. The back saves the data and decides who's allowed to see it. Building that yourself means servers, a database, password resets and a lot of lost weekends.
A BaaS hands you the back already running. Base44 is one. Every app comes with entities for data, logins, row-level security, backend functions and integrations from day one.
The picture I use is renting a furnished flat. You still choose where the sofa goes. You just don't fix the boiler.
I made a free course about it, What's BaaS? (opens in a new tab): twelve five-minute lessons and a playground for trying SDK calls without breaking anything. No code needed.
Related:Entity, Backend function and Row-level security.
Where I've used it: