The French expression faire un bœuf (“doing a beef/ox”) means to jam or have a jam session. A jam (session) can happen at any time when musicians get together and jam, or play and/or sing in an informal or improvised way.
Why do they say faire un bœuf though? What does improvising music have to do with oxen or beef?
Well, it comes from Le Boeuf sur le Toit (The Ox on the Roof), a celebrated Parisian cabaret-bar founded in 1921 by Louis Moysés. In the 1920s and 30s especially, it was popular with musicians and singers, and improvised jam sessions often broke out there. Such activities have been known as bœufs ever since. The bar still exists, but is now a fancy restaurant and apparently no longer has the glamour, social cachet and bohemian atmosphere that it once had [source].
It is not known why we call such activities jam sessions in English. Apparently jam was first used in this way in the 1920s among jazz musicians. Possibly because it involves muscians getting together in one place, e.g. jamming themselves into a room. Or jam might refer to something sweet or a nice treat, which was one meaning of the word that emerged in the 19th century [source].
I’ve played instruments and/or sung in jam sessions in pubs, boats, trains, churches, vineyards, gardens, community centres, castles, fields, airports, mountains and other places. There are always great fun and I miss them.
Here’s a video from a folk music session that used to happen in Tafarn Y Glob, a pub in Bangor, and will start again one of these days, hopefully:
Are there interesting ways to refer to jam sessions in other languages?