No 'slang' term really has an actual definition because of its origin from the streets, it can mean anything from anywhere really..
My definition however is basically a mentality. I've met a lot of hardcore O.G.'s (in my opinion at least) and with all of them you HAVE to keep a good level of respect around them, don't joke around about anything really. Keep your voice and tone appropriate, don't get emotional, don't show weakness, don't touch them (minus fist bumps) don't do gay shit like play fight and all that. It's like playing a character. Respect is #1
Business is business. #2 is loyalty, don't screw a gangsta over, they will go out of their way to make their point clear, and they will jump you with your back turned. Once you make it a war, you're knee deep in fuckery, expect a brick through your window at 4:00 am.
Personally I dress like a 'gangster', I like the style. I can't stand these 1990's kids tight jeans, converse, flamboyant checkered, furry snap back OBEY bullshit. Baggy jeans phase may be over, but I am not tightening my testicles for the sake of fashion.... And people usually judge me before they know me, they think I'm scary because I always look pissed or I may have a gun, but it's just a persona, I'm a really cool guy. I just got tired of getting robbed in high school lol. Now I often get other thug looking people asking for cigarettes or weed and i just say "sorry bro" and move along.
It's not a look in my opinion, you can have a sheep in wolf's clothing.