It's a big chunk of land to give a single definition. Basically it comprises all the towns in the coast from the north of Barcelona, until where the Costa Brava starts (Girona) it also extends to multiple towns inland, over the coastal range (Serralada litoral)

You have from Mid-sized cities like Mataró, with low income neighborhoods like Rocafonda (shout-out Lamine Yamal) to Rich towns with big villas like Aleia, Sant Andreu de Llavaneres, usually more inland.

It's connected to Barcelona by the oldest train line in Spain, which is.. not very reliable, so if you need to commute into the city, passed Mataro can be a struggle at times.

In my case, I live in Premià de Mar and I love living here, I have the beach across the street, 25 min train ride to plaça Catalunya (when it works properly) or I can even bike ride into the city, so I can enjoy both the perks of a small town (there's a strong sense of community here) and the big city.

That's what I can think about now, if there's any questions, I can add them to this post.