Opuntia indica, also known as the prickly pear cactus. 
In the wild these cacti can grow up to 15ft tall! As it's a cactus this plant doesn't take very green fingers to look after it. Place it somewhere very light. Direct sunlight is fine. Water when the soil is completely dry. Easy peasy!
The plant comes in a 17cm diamater nursery pot and stands approximately 45cm tall. Please note: although nature is incredible, not all plants will ever be the same. Therefore please expect some variation in plant colour and shape from listing images.