exclusive or non-exclusive license

this is still foggy to me, can someone explain the two?

Exclusive - You agree to deal with only one party.

Non-exclusive - You can do the same deal with multiple parties.

If that isn't clear you will need to be more specific about what it is that is foggy.

so when licensing a image to client for commercial use, if im taking the picture FOR THEM, its exclusive, if someone comes to me and wants to use my images its non-exclusive in that i can license out to others if i choose?

Not necessarily. If somebody comes to you and wants exclusive rights to one of your images, that can be written into the contract, usually for an additional fee. If they don't need exclusive rights to the image, THEN you would be able to also sell it to somebody else, ideally making up for not getting as much money from the original purchaser.

As you suggested, shots you take for a specific client will pretty much always be exclusive for them. Shots you take on your own for stock or on spec (speculation) can be either exclusive or non-exclusive depending on what deal you work with the purchaser. Obviously if you've already sold an image to one customer and then somebody else wants exclusive rights to it, you can't go back and un-do the original deal, but you might be able to agree not to sell it to a 3rd customer.

not so foggy anymore, thanks!

Don't forget that you can offer an exclusive licence for a set period of time, and then it can become non-exclusive once that period expires.

and some clients (like publications) might specify an embargo period in which they have exclusive rights to publishing the images taken for them.

And the usage sold to a client--whether exclusive or non-exclusive--might be limited by time or area, in which case you can still sell it outside those limitations.

A client might, for instance, have exclusive use for only one year, after which he no longer has any use and you can sell exclusive use again to another client, making sure the client is aware that someone else had use of it earlier, but will not have use at the same time.

Such things aren't done so much with still photography, but are done in literature and television quite often.