People are being very technical and most of what is written is true. Being the spawn of alcoholism on both sides of my family through my grandfathers and my father, and having abuse issues with alcohol and some minor drugs myself, I think I can answer this with important and layered detail.
First off, alcoholism and alcohol abuse are VERY different. Let that not be mistaken. I've read a lot about alcohol abuse eventually leads to alcoholism, which is true, but it's not even close to being that simple. College frat parties have students that engage in alcohol abuse. They are drinking to get drunk. Someone who relies on alcohol to function is an alcoholic or has the disease of "alcoholism". These distinctions cannot be overstated. What do I mean by function? I mean, this person usually drinks before he does anything, or wants to do anything else for the day. And usually, it's not just having a couple drinks before they start their day. It usually entails drinking before, during, and after their day is 'completed'. And like these guys said before, alcohol interferes with everything. They won't function as well at work, they will ruin social relationships that were thriving before alcohol became #1; their anything and everything in their lives. I've engaged in plenty of alcohol abuse in my life. Every weekend come Friday and Saturday me and a few buddies were always in college mode, drinking to get hammered. If someone is an alcoholic, there is a good chance they are using other drugs as well. Whatever gives them a brain altering buzz could be an issue, as it numbs them and allows them to escape whatever anger, sadness, guilt, or grief they are feeling.
Another big distinction is the every day drinking vs. drinking to get drunk. You can be a social drinker and drink every day. That doesn't necessarily make you an alcoholic. By the same token, you can drink once a week and be an alcohol abuser or even an alcoholic. I have a family member who is an alcoholic and doesn't drink at all because, they tried it once, and got completely out of control and was an embarrassment to him/herself and everyone who knew her. I guess I'll state it as the comedian/actor/alcoholic/addict Robin Williams put it. You aren't an alcoholic if you like to get drunk. You are an alcoholic if when you get drunk, you never stop drinking, and you do a lot of stupid things, most notably drive. And anytime you drink, you do stupid things, can't stop drinking, and drive. So. Need alcohol to function, can't STOP drinking or being an idiot or stop yourself from driving = alcoholic. Also, angry drunks are usually alcoholics because they are drinking to hide some pain they already possess deep down. (Not yourself). Drinking to get drunk and acting goofy but knowing enough to not drive but acting like a funny version of yourself, while still drinking a lot, more than 2-3 days a week still is alcohol abuse. It's really about how alcohol affects your overall well being. Blackouts every time you drink or getting into fights every time you drink means you are 99% surely an alcoholic. So don't fret if you think you drink a few more than other people, you could just enjoy alcohol and like having a good time. Just don't get behind the wheel and take into account how you treat yourself and others while you drink. If alcohol gives you a lot of problems, you're probably an alcoholic.