I would say "normal" is a statistical point of view. A normal (gaussian) distribution is a bell shaped type of curve. If you look at the mean ± the standard deviation, you get around 70% of the population. So a large majority of the population is within mean ± sd.

There is also a social dimension to "normal". What is currently considered acceptable is within the "normal" distribution of the population. What is outside is considered not "normal".
Of course, all of this is at the population level.

As far as the gay thing, my guess is that is was not considered as "normal" because not falling into the overall common, average (70% limit) group. These are numbers only. I'm not being rude to anyone.

One interesting point, and sorry, I have been looking where I read that and could not find it, when a group reaches the 30% threshold within the population, its is not discriminated against so heavily. It gets closed to the "norm", the "average".