Cotton is a plant that grows the soft, fluffy fibers that are used to make the fabric also known as cotton. Cotton grows best in very warm climates.
Cotton is a hugely important fiber, since it's used to make all kinds of clothing, bedding, and other things we use regularly. Your t-shirt, jeans, underwear, and socks are probably all made, at least in part, from cotton, and so is your bath towel, pillow case, and the curtains on your windows. If you use cotton as a verb, it's an informal way to say "take a liking to." This meaning has a Welsh root, cytuno, "agree."