Folk dance is similar to barn dancing, or country dancing but on the whole tends to be slightly less energetic, and often contains more complex figures.
There are a number of folk dance clubs in Oxfordshire - mostly they meet on a weekly basis and charge a small subscription. The music varies from using recordings, through one or two musicians, to a whole band. Clubs are very welcoming to new members, including complete beginners - although one or two are specialist events and will expect a certain level of knowledge. If you've never done it before it's best to check the expectations beforehand. There will usually be a break for tea and coffee, and sometimes a bring and share supper.
The Oxfordshire Folk Association is an umbrella body co-ordinating social dance in Oxfordshire, and they often organise events in their own right. Their website also contains some useful information about the different styles of dance available.