Realism is an approach to life that means dealing with the way things are. If you see the world through the lens of realism, you accept what's in front of you and don't pretend it's otherwise.
For those who follow the doctrine of realism, it's "just the facts, ma'am." What you see is what you get; if you can't see it or touch it, it doesn't really exist. Realism is more than just a way of approaching life; it is a formal philosophy and a 19th-century art movement, where animals and people and landscapes are depicted as they appear — no purple and green faces or polka-dotted ponies, just people and trees and landscapes painted in proportions and colors that look like the real thing.