The term "homesteading" can mean a lot of different things. It used to refer to the government program under the Homestead Act, where pioneers could settle on a piece of land and "prove it up" over a period of years, making it sustainable and profitable. Then, they would earn ownership of the land.
Nowadays, homesteading applies to anyone who values sustainability and self-sufficiency and strives for it. This incorporates growing one's own food, whether entirely vegetable-based or including animals, and for many, producing one's own power.
"Urban homesteading" takes this idea one step further. People are striving for self-sufficiency and living a simple lifestyle in the city, drawing on ideas of sustainable agriculture, permaculture and voluntary simplicity.