Spec Ops.
Special Operations Command or 'Spec Op' is the overall unbrella which contains each branch of the service's various 'unique forces' [special training and skills in combat situation more than the average soldier, sailor, airman or marine].
It contains, to name a few: US Army: Special Forces ['Green Beret'], Rangers, Delta Force, Rapid Deployment Teams, and some acpects of the Airborne community. US Navy: BUDS/SEALS. US Air Force: Combat Controller, Forward Combat Observers, etc. US Marines: Marine Force Recon.
These various unit will work independently of each other ot together in concert to accomplish mission deemed non-completeable by conventional means: like being deployed as a 'forward watch post' just outside of Bagdhad waiting for Hussain to leave the city so that he could be 'netrulized'.
'White Operations', I guess you could call them even thought the term doesn't exist, are you more open missions that you'll hear about in the news as the or just after they've happened with one of these types of units, like freeing a foreign embassy somewhere. Done out in the open with no 'nasty' repercussions. A missions that required very special skills that any of these units mght have.
'Covert Operations' or 'Covert Ops' are the quite type of sneak in/out missions that you don't want anyone to know about at the time or maybe for a time after, but you can probably sleep well at night and look yourself in the face in the morning. You could classify some of SG-1's repeat recon missions as 'covert op' missions. They know that there are baddies there and they're going back to get more info without being caught.
'Black Operations' or 'Black Ops' are more of a 'kind' of operation... the kind the government and/or the military really doesn't want folks to know about at the time [like my friend above] or ever. They are the 'sneak in, snach a Somalia rebel leader and bring him out under the noses of his people' sorts of things. Or, as Jack so simple worded it 'some damned distasteful things' such as asassinations, etc. that are not considered 'nice' by the world at large.
What the world at large won't acknowledge is everyone does it. They just don't want to talk about how they get all their wonderful insode info.
So... I's say a simple analogy might be:
'Spec. Ops' is fruit.
'White Ops' are apples - simple, up front and familiar to everyone
'Covert Ops' are kiwi fruit - not as commonly known, but okay
'Black Ops' is the razor blade someone stuck in one of the apples.
I hope this makes some sort of sense. It's hard to explain something I've kind intuitively know for many years. {It also doesn't hurt that my husband is ex-Spec. Op's. Special Forces...}