Catnip is a plant. You can buy seeds in a packet just like any other plant or flower at a greenhouse or other such facility. I bought some for my cats and planted it in my backyard and much to my surprise it flourished in the dry, hot Colorado weather. I had a huge bush of it for the longest time. It was useful because whenever my cats got out they were drawn to it like a magnet, and they'd sit there, cracked out, until someone came and picked them up.