What is this 5.11 Jacket Thingy?

I read about somewhere a word called 5.11 Jacket I have been wondering what it was about. Later, I discovered from http://www.lapolicegear.com that this is some kind of special jacket or gear that gives safety and ease at the wearer.

One sample of that 5.11 jacket when i searched how it looks like. There are more variations available actually.

According to that website I mentioned up, this jacket is an outerwear that offers functional innovation and that allows one to reach his/her peak performance on duty with a perfect blend of tactical/practical functionality and traditional style. Whether one needs light coverage for mild weather or for more severe winters, lapolicegear has them too. Moreover if people on duty needs to be seen, there are also new high-visibility items, a waterproof parka, and a waterproof, insulated, reversible 5.11 Tactical jacket.

Now that I have seen how it looks, what is the purpose, and what are the variatins when i searched for the photos, now I know wh can use this and what is its importance in terms of smeone's safety.