Otsumami おつまみ: snacks, usually to go with drinking alcohol or soft drinks.
You will see these types of snacks many places, usually by the alcohol section of the grocery or convenience store.
It comes from the word tsumamu つまむ, which means “to pinch” but can also mean “to pick up with fingers or chopsticks.”
It really is not anything specific, just sort anything easy to eat while drinking (beer, alcohol, or even just soft drinks) can be considered otsumami. You could include any kinds of appetizers, finger foods, light snacks, and tapas as “otsumami.” I usually think of things like arare or senbei, but many other things like cheeses, dried squid, edamame, tsukemono, and all manner of appetizers are described by the word “otsumami.”
Often on the airplane, I am given a small bag labelled otsumami, usually some sort of arare, dried peas, or kaki-no-tane. So I don’t always associate otsumami with drinking alcohol necessarily, rather I think of it as a salty snack food.
In Okinawa, a popular otsumami is mimigaa ミミガー (dried and shredded pig ears); to be honest it does not look creepily like pig ears, so if you don’t read Japanese or are unfamiliar with Okinawan words, you probably would not realize exactly what you are eating. I like an otsumami made by Orion labelled “beer nuts”: ビアナッツ. They even sell it as a small omiyage. When you are in Okinawa, you should try some of these Okinawan otsumami.