A Party Ring is a popular type of biscuit (cookie, to Americans) in the UK. They are a flat, hard biscuit with a hole in the center, looking something like a small donut; however, they exist primarily as a vehicle for brightly colored frosting; in this case, bright pink, purple, orange, yellow, and white striped with drizzles of contrasting colors. They look delicious, until you consider their actual components, after which they sound only okay. Being American, I do not know how they actually taste, but by report they are nothing special.
This biscuit was introduced by Fox's Biscuits in 1983 with the intended target audience of children, although they have since become a suitable treat to serve in the tea tent at a village fête. They will remain fresh and cheerful over a long afternoon, and not disappear too quickly, as they are not too delicious. They are suitable for dunking, particularly in those settings where the quality of the tea and biscuits is secondary to the presence of tea and biscuits.
Party rings originally took advantage of new 80s dyes that produced particularly bright colors, although in recent years the colors have moved towards pastels. Regardless, they exist primarily to remind your hindbrain of big, delicious candies.
Thank you to Auduster for helping me with the finer points of British culture.