Hi,
This is an Opuntia, a rather easy cactus to care for, but it needs full sun outside and not in the house. Cacti are no houseplants. Also an Iron pot is far from teh ideal situation. A plastic or clay pot with draining holes in the bottom is better. I guess the bottom of the plant is already dead (rotted?). Cut a healthy part, let it dry for some weeks wand repot it in a well draining mix.
HTH
Pieter

Pieter is correct! You need to get that poor thing into some sun, but gradually. The Bottom (older pad) appears to be dead and dried out and it appears to have been receiving a real Lack of sunlight. That is the reason the new growth is so long and pale. What you could do is as Pieter said, Cut a piece off and let it sit for about two weeks to form a callous over the cut end. It may, during that time even start sprouting roots from the side that is faced down. That's fine. If it does, then just lay it on some soil (in a clay pot), in a very bright spot outside. Direct Sunlight WILL Burn it... so under a tree would be ideal. Once it takes, it should send out a new pad. Slowly start moving it into more and more direct sun. In Pots, I water my cactus when they're growing, whenever the soil feels dry... But I'm in Tampa so it gets pretty hot here. But if the soil feels dry, water it a bit and it should be happy and should really recover nicely. DON'T Let it get Soggy! Once you have some nice new growth, I'd cover the soil over the old lanky growth so the only part showing is the new, healthy growth! Since you don't know exactly what type of cactus it is yet, I'd bring it in during the first winter, then move it back out after the last frost(usually after Mothers day) next spring. If you happen to get more than one piece to take off and look good, You Could try leaving one outside over winter. A lot of cactus can actually take the Cold of winter... It's the Water that kills them! SO, if you create a cactus bed, it may make it. If you decide you want to try a cactus bed, let me know and I can provide you with some links. Or, you can do a search for "Cold Hardy Cactus" and probably find plenty of sites ;-)

Picture of the cuttings.

Here is a link that might be useful: