I found this pad growing in a field by my house so I took it and planted it. Now I want to feed it to my tort. What type of cactus is it, and is it safe to feed to my tortoise?
Spineless opuntia. Its an excellent food source for tortoises.
Smaller tortoises, like the one in your avatar, really like the small tender young pads, like the top and left ones in your pic. I'd plant a bunch more of these so you always have those young pads ready to go. You can feed this two or three times a week with no problem.
Mine all love the stuff. Just a warning, it can cause their poo to be a bit slimy/watery. So, if you see that, its no need to worry, its just the cactus.