This would be known as an herbivore. Their diet consist solely of plants, not meat. A few great examples are cows and sheep.
An easy way to remember this is when you look at the word herbivores it has the word "herb" in it. If you can remember that an herb is a plant it will be easy to remember that herbivores only eat plants
Hope this helped!
~Just a girl in love with Shawn Mendes