Opuntia is the name of a genus of edible cactuses originally from the Americas which are now grown world wide both as ornamental plants and as a food source.
The entire opuntia plant is edible, the green parts are usually sold in North America under the name nopales while the fruits are known as prickly pears.
I have never had the opuntia greens since I have no idea how to prepare them, and they are not particularly popular here in Toronto. The fruit is readily available in grocery stores when it is in season and I do like prickly pears in spite of the fact that they have tiny needles all over them and they make peeling them literally a pain.
It is not just us humans who enjoy eating opuntia cactuses, if you are a regular reader of thios blog and followed the links to the instructions how to care for most of the land tortoises mentioned on this blog, you will find that a recurring suggestion is to provide them with opuntia as part of their diet.