What does "rookie cop" mean anyway?

I keep reading that the cop who shot Tamir Rice was a "rookie cop." It was also a "rookie cop" whose gun discharged and killed an innocent man in an NYC apartment building (and then disappeared from his department for six minutes while contacting his union representative).

So what does "rookie cop" mean? The WaPo article quoted below seems to say you're still a rookie 2+ years after first becoming a cop, or at least through month 9 of the last force you worked for. When does one stop being a "rookie"?

Or is "rookie cop" really just about deflecting blame from the officer? A way of saying they had some right to be unusually clumsy, jumpy, scared, etc? Is the popular media wittingly or unwittingly helping to shape these stories into pieces to engender sympathy for these (poor, inexperienced) cops?

The Washington Post writes:

"Before rookie cop Timothy Loehmann, 26, became yet another symbol of the tensions between law enforcement and the black community, he was an eager graduate of the City of Cleveland’s police academy in March.

In some ways, it was the big leagues, his father told the Northeast Ohio Media Group in an interview.

He was tired of the sleepy policing of the suburban district in Independence, Ohio, where he had worked since 2012. He reveled in his new assignment in one of Cleveland’s most violent communities, the Fourth District."

Why aren't minorities carrying openly?

The way I see it, the next time some group of hillbillies starts flaunting their second amendment rights, groups of minorities should pick up their legally-owned firearms, walk right over, introduce themselves, and join right in.

Why can white freaks parade around with assault rifles, but a twelve year old black kid with a toy gun doesn't last a minute after a cop arrives?

When I was twelve, we ran all over with all kinds of toy guns, even bb guns. Never worried about such a stupid, terrified (chicken?) cop thinking I might be some threat.

Granted that was the eighties. But those white trash guys with real guns aren't being shot these days either.

So if minorities got out and open-carried more often, maybe white people would get used to it.