Krog means 'pub': a place that will usually serve both food and drink, but where the focus is often on the drink, as opposed to a restaurant, where you would usually need to order food. You use it with the preposition på, but the expression gå på krogen (literally 'go to the pub') can be used just to mean 'go out drinking' rather than referring to any specific place
Hear how krog is pronounced in the audio clip below:
Most European languages make a distinction between pubs (also called taverns in older English) and food-focused restaurants, which are a newer invention. Krog comes from the Old Swedish word krogher, which comes from an even older Germanic word.
A traditional krog would offer only classic husmanskost (roughly meaning 'everyday food') such as meatballs and mashed potatoes, or other meat-based fare.
But these days, the distinction between krog and restaurang (restaurant) isn't so clear. Many eateries with the name krog might actually serve quite elegant food (you could refer to them as a lyxkrog or 'luxurious pub'), and you'll also find krogar serving food of many different cuisines: you might hear about an indisk krog (Indian pub) or fransk krog (French pub), for example.
You'll also see krog pop up in plenty of compound nouns, such as krogrunda (roughly 'pub crawl': an evening spent visiting multiple pubs); krogliv (pub-focused nighlife), krogmiljö (pub environment). As you can tell, it's a word that evokes a specific and traditional kind of socializing, much like British pub culture. Another compound noun you might hear is krogbråk (an argument or scuffle that breaks out at a pub).
And if you ever find yourself on a road trip around Sweden, you should look out for a vägkrog, literally meaning 'road pub'. These are pubs located close to a busy road, where you can often stop and get a warming bite to eat quickly before going on your way.
Det finns en mysig krog i stan
There's a cosy pub downtown
Jag går på en dejt på en krog ikväll
I'm going out to the pub for a date tonight