The direct translation of the title '엄마 친구 아들' / '엄친아' ('Umchina' for short) would be <Mother's Friend's Son>, but it also has another meaning.
In Korea, 'Umchina' can also be used as a slang word. '엄마 친구 아들' or '엄친아' refers to a person who is perfect in everything: abilities, appearances, and backgrounds. It's usually used by a mother to motivate her son / daughter to do better by comparing him / her to an obscurely perfect character.
[*You can use this for a person you think might fit this description, he doesn't have to actually be your mother's friend's son.]
For more details, refer to: https://www.reddit.com/r/DoesNotTranslate/comments/7y6zmr/korean_umchina_%EC%97%84%EB%A7%88_%EC%B9%9C%EA%B5%AC_%EC%95%84%EB%93%A4_signifies_a_person_who_is/