What is an Eunuch? Is Marriage for All? Matthew 19:9-12

Mat 19:12  For there are some eunuchs, which were so born from their mother's womb: and there are some eunuchs, which were made eunuchs of men: and there be eunuchs, which have made themselves eunuchs for the kingdom of heaven's sake. He that is able to receive it, let him receive it. 

Mat 19:9  And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery.

Mat 19:10  His disciples say unto him, If the case of the man be so with his wife, it is not good to marry.

Mat 19:11 But he said unto them, All men cannot receive this saying, save they to whom it is given. 
 

Dan 1:9  Now God had brought Daniel into favour and tender love with the prince of the eunuchs. 
Dan 1:10  And the prince of the eunuchs said unto Daniel, I fear my lord the king, who hath appointed your meat and your drink: for why should he see your faces worse liking than the children which are of your sort? then shall ye make me endanger my head to the king. 

Isa 56:3  Neither let the son of the stranger, that hath joined himself to the LORD, speak, saying, The LORD hath utterly separated me from his people: neither let the eunuch say, Behold, I am a dry tree. 
Isa 56:4  For thus saith the LORD unto the eunuchs that keep my sabbaths, and choose the things that please me, and take hold of my covenant; 
Isa 56:5  Even unto them will I give in mine house and within my walls a place and a name better than of sons and of daughters: I will give them an everlasting name, that shall not be cut off.