It was a custom in some ages of the Church to hand down, as punishment, a restriction on eating meat and drinking wine. However, this punishment was often lifted on Sundays. At the council of Tribur in 895, lead by several Archbishops under Pope Sergius, it was declared as a penance that the: "penitent might not eat meat nor drink wine, except on Sundays and festivals."
(Landon, E. H. (1909). In A Manual of Councils of the Holy Catholic Church. Edinburgh: John Grant.)
image via wikipaintings in the Public Domain. The Council