My understanding (which might be wrong) is that in the middle ages only wealthy people actually owned a horse(s) but but in later times even middle class people owned a horse(s).
Assuming that's correct, where did they keep them? I've seen stables in these old large estates that were owned by the wealthy, but what about average people?
Livery yards, where in pretty much every-town and sort of a necessity, kind of like payed parking lots in major cities, people would pay a weekly/monthly fee to keep their horse there, there were different kinds of Livery yards as well which offered varied services, some would feed, exercise your horse for you, others would require the owner to feed and take care of the horse himself (These as you probably already guessed where cheaper) some even offered discounts if you allowed your horse to be used for work, such as a horse for a riding school