[MikeTheGreat]

I'm still figuring this out myself, but I think that people are talking about race in at least two different ways:

1) Race from a biological/chemical perspective. Stuff like 'DNA determines race' goes here.

2) Race from the perspective of all the things that happens to a person because they belong to a particular race (as defined in 1). Apparently, being black and driving in America means it's more likely that you'll be pulled over by the cops, more likely that they'll assume you're a drug dealer, etc, etc. I wouldn't know because I'm not black, and every time I was pulled over by the cops I was clearly at fault. Differences like these are discussed under the umbrella of 'race'.

The key is that in the second case there's nothing from biology / chemistry / science that says that black people should get pulled over more. That's just how things are in America now - it's a "social construct".

Again, I'm not an expert, but I think that's what people mean by 'race is a social construct'