there's monolith web applications, what's the opposite of it called? the RESTful ones.

RESTful? It's the mixture of concepts you did here.
I'd say an opposite to "monolith" is "polylith" or, in your case, micro-services.

What @vintprox said.

Microservices are pretty standard inversion of monolithic architecture.

There is even O Reilly book
For all fifty shades of gray in between

Worth noting that a micro service is just a subset of service orientated architecture. You can also have a modularised single solution which I don't believe we would call a monolith.

@Crost the book fifty shades of microservices is covering it too.

@vintprox so my backend API (golang) and frontend (vue) - is it microservice?

@minsomai no. Frontend is frontend.

Backend is service oriented. Does your backend maintain multiple business processes? For example, does it perform; user management, sign up, data retention(file attachments), and other business related logic.

If yes, congrats! You have a monolith!

If your backend is built of multiple separate dedicated services that interact with each other through integrations and had dedicated databases(sometimes), then you have microservices!

@sariel thanks for the clarification. and I learnt that the correct term for my type of app is called RESTful architecture or N-layer architecture.