Pluto is an object that orbits the sun just like Earth. Some people call it a planet, because it orbits Earth just like Jupiter, Earth, Saturn, etc… , but some people don’t think it’s big enough to be a planet because it’s smaller than all of those. They call it a “planetessimal” which means “small planet”
Pluto used to be a planet. It got demoted recently, as it has a very eccentric orbit. It takes it above the normal plane in which the other planets orbit in an eliptical loop that comes in as close as Neptune! There are also many other objects on the outer fringes of our solar system that are larger than Pluto and so could be considered planets. There is a whole ring of objects surrounding our solar system called the Oort cloud. This is the source of most of our comets. Occasionally gravitational wobbles pull an object out of place and it starts to fall towards the sun.