Wellies is a short name for Wellington, which refers to a style of pull-on boots. Wellies are made of rubber and are worn in rainy weather or muddy environment.
Wellington is th e common British term for "rainboots.” Wellies are most often used during open air musical festivals in Britain, like the Glastonbury Festival
Among the celebrities wearing Wellies by Jimmy Choo and Hunter during the 2009 Glastonbury Festival were: Pixie Geldof, Jo Whiley and Naomi Campbell, Daisy Loewe, Lily Donaldson.
Author's Note: If you need Wellies, visit Hunter's website https://www.hunterboots.com/de/de_de/, seems to be that in Europe they are the best makers of Wellies