Socialization by definition is the ability to function in society. No where does it state that you must learn from your peers how to behave like a functioning member of society.
That said the term is often alluded to in the course of conversation with non-homeschoolers as a much neglected area in a child's development when homeschooling. It is a silly question really as one knows you learn social ability from the world you interact with not from kids your own age. If in fact the person asking means will they have friends. Then they should be posing their question as such.
Will my kids have more or less friends as a homeschooled child. That depends on my ability to get them out there in other groups. My ability as a parent to allow them to drop their homeschool studies during the course of our summer to play with other kids in the neighborhood. It depends on my children's individual personalities, their likes and dislikes in relation with other kids. It depends on a great many factors which are only slightly different to a Public Schooled child's factors on whether or not they will have successful friendships.
What I can say is my kids aren't shy. When they want to make their presence known they will and stand back they will take you by storm will their robust personalities. Are they one hundred percent well behaved. No they are aren't they are children, I ask you to show my one who is. I want them to be the individuals they were meant to be not cookie cutter, school hating kids. And if that seems harsh that's just my opinion and we all have our own. And so if you see me in the street and ask 'what about socialization?' I will likely say 'what about it?' It's a point that has no point and therefore needs no more discussion on it.