To get the idea over, call it whatever you like. The most common word these days is “Ceilidh”, pinched from the Irish and Scots Gaelic, and pronounced "kay - lee". It means dance & music, so that's what I'm going to call it here.
-Barn Dance is another very common name. Folk Dance is OK, if a bit twee. People also like English Country Dance as a title. Country Dance alone may get confused with American countree-and-western. Yee - ha!
You may have a committee whose help you'll need with jobs, or just people to sell tickets to. Even if you're running a "compulsory attendance" ceilidh at a wedding reception or birthday, you'll need to give guests the novel idea of them having a good time by joining in and dancing, rather than just by watching (and sometimes getting tipsy at weddings).