Imbiss is a general German term for small food stand or street food shop, usually tiny and locally run (often a family operation). There are thousands of imbisses around Berlin, serving everything from the standard currywurst, pizza, or döner kebab to the more exotic such as Nepali vegetarian dishes, Russian red beat soups, Copenhagen-style hot dogs, and Korean food.
What most imbisses have in common though is their basic decor and emphasis on functionality over fancy ambiance. You should, however, never see this as sign of lacking atmosphere—it's all there, but with food as the central focus.
Germans love their imbiss for an on-the-go meal or takeout. There is also an army of small mobile imbiss-like food stands at the train and Ubahn (metro) stations offering fresh Brötchen (bread roll) with cold cuts, steamed bratwurst, coffee, and beer (remember, we are in Berlin) to go. An imbiss will usually have quite cramped seating inside for a handful of customers, mostly used during winter. In the summer time (April through October) people will flock outside for a quick lunch or dinner, and small talk.
What makes Berlin attractive from a culinary perspective is this vibrant, multicultural, relatively inexpensive and ever changing food scene. Berlin (which won 13 Michelin stars in 2011) is usually not associated with an outstanding food culture beyond the clichéd beer and sausage, which is a shame. German food is as varied as say French or Spanish., and Berlin offers a United Nations of culinary experiences. Let me highlight a little Korean imbiss near my apartment which perfectly illustrates this.
Ixthys is located at Pallasstraße 21 at the corner Goltzstraße in Schöneberg, bordering Kreutzberg. This tiny, rather inconspicuous imbiss seats only ten or twelve but serves some great kimchi, hot and spicy soups, and bibimbap.
After a four year stint in Jakarta, Indonesia, I generally find the Asian food scene in Berlin to be a somewhat flavorless, watered-down version of the real deal. Sadly, this is not just a Berlin phenomenon, but true for much of Europe. A majority of Europeans don't like their food too hot or spicy and restaurants adjust their cooking accordingly. Though most Asian restaurants in Berlin do offer the typical table jar of hot sauce—be it some sort of chili ketchup, sambal olek, or sliced chilis in oil—it doesn't reach the same tongue-searing levels.
But Ms. Young-Ai, the elderly Korean women who runs Ixthys, dedicates much attention to brilliant, authentic Korean cooking. I recommend their hot Kal-Guk-Su (about $8), a Korean noodle and veggie soup in chicken broth, and their homemade kimchi on the side.
Pallasstraße 21, 10781 Berlin, Germany (map)