In this line, Adam is referring to Eve, after learning that she had eaten the forbidden fruit. He calls her fairest creation because he is obviously in love with her, and feels that she is God’s best work. In the OED, fairest means pleasing to the eye because of fresh, charming, or flawless quality. It is not a surprise Adam feels Eve is fairest. The OED also describes creation as the act of bringing into the world or ordered existence. Eve was a direct creation of God. It is very fitting for Adam to call Eve fairest creation. Both words in the title serve to describe her.