The formal MOS classification for an Intelligence Analyst in the United States Army is 96B. Our main purpose in the Army is to act as a massive filter for Intelligence. We take in varying types of Intelligence from a variety of sources. Some examples are: COMINT or COMunications INTelligence which deals with communications intercepts from enemy communication systems, SIGINT or SIGnals INTelligence which is intelligence taken by scanning for the enemy's radar and EW systems, IMINT or IMagery INTelligence which is actual snapshots or video feeds of UAV's or Sattelites, and HUMINT or HUMan INTelligence which is taken from captured prisoners, Counterintelligence Agents operating undercover, or by simple slip of the tongue.
Now, what do we do with all of that? I'll give a brief example which should make more sense than giving you a complicated definition that is little more than a collection of large words will little common sense behind them. Suppose that friendly forces, i.e. US forces are engaged in a ground war in nation of Kerplankistan (only fans of the Simpsons will catch that one). I am an Intelligence Analyst for the 7th Armored Division. The enemy force that my unit is tasked to attack is the 33rd Brigade Tactical Group, a Brigade sized element composed of two battalions of tanks, let's say T-72's, and one battalion of mechanized infantry (infantry that are carried in IFV's) that are equipped with BMP-3's. As we move to attack North, I recieve a IMINT report stating that they saw 7 tanks moving Southeast in a spearhead pattern. Well, 7 tanks = one tank company, which an enemy tank battalion has 3 of. Now that I know where one is, I can make an estimate, based on the terrain and my knowledge of my opponents tactics, of where the other two may be.
Now, as I plot these on my map, I template where the other two may be. My General then makes the apporpriate changes to our plan and moves friendly units to engage. A few minutes later, I recieve a SIGINT report that we have located 2 counter-battery radars (a radar used to track incoming artillery rounds and pinpoint their origin to fire at them) just Norht and West of where the 7 tanks were spotted. Looks like I've just located the enemy's Artillery Battalion. Immediately, I tell the Fire Support officer and we drop a whole lot of steel on target (i.e. we fire off two or three concentrated artillery strikes with haste). Based on the location of the Artillery Battalion, I assess that the enemy's support element (beans, bullets, fuel) should be about 15 Kilometers behind that artillery group. I tell my General what's up, and he sees that as a viable target for CAS (Close Air Support or AI - Airial Interdict). The Air Force targeting officer get's the grid where I think they're at and we send two A-10 Warthog's to eat the enemy alive.
This is not all of what we as Analysts are capable of. At higher echelons we do LIC (Low Intensity Conflict) analysis, i.e. political assesments, country studies, arms buildup analysis, etc. While I was in Kosovo I did a lot of LIC analysis concerning key leaders and drug trafficing. We are Mentats, pulling a wide variety of facts and rumors together to make a clear, common picture of what's really going on, like a human computer.