Spain has more land cultivated with grape vines than any other country in the world, and only France and Italy produce more wine. But beer is much more popular here than it is in those other countries, and there are a lot of places to drink it. It's something of an American invention, really, that tapas and pintxos are the provenance of wine bars - more often they are eaten with a glass of beer.
Technically, cerveceria means brewery, and a few of Barcelona's establishments actually do brew their own beer. But in general, the difference between a bar and a cerveceria is pretty slim - something like the line between a cafe and a bistro. Food is a big part of the distinction, as some bars don't have food but almost all cervecerias do. In effect, the best translation might be "pub."
One of the best things about cervecerias is that they're open through much of the day and night, meaning that one can have a beer and a bite to eat whenever the need arises. The food can be heavy or light, but is almost always something small. Cargols, squid, shrimp and cuttlefish are popular; sausages and meatballs are ever present. At larger places, the selection can be overwhelming, the creations exotic. On the other hand, the plates are often as simple as this - a few roast peppers sprinkled with sea salt.
Barcelona has a long history of brewing. The small Moritz brand was originally from here - but is now bottled in nearby Zaragoza. The company - which was founded in 1856 - was only recently resurrected, after nearly four decades out of business, and has enjoyed something of a cult following among chic locals, who extoll its pale malt and lemon flavors. Ask for a beer in most places, though, and you will almost certainly be given an Estrella Damm. Estrella, also local, is one of the largest brands in Spain, and is a brew usually drunk without analyzation.