The evening is the last part of the day before night falls, just when the sun is starting to go down. Most people eat dinner in the evening.
The quiet, winding-down, ending part of a day is the evening — you might also call it "dusk" or "twilight." Some people define the evening as the time after dinner and before bedtime, and you can also use the word to talk figuratively about the final part of something else: "It was the evening of his life." The Old English root of evening is ǣfnung, "the time around sunset."