I assume the cliënt wants an unbound, (not quite sure what the correct english legal term is, I'm Dutch) restrictionless license which will grant them the right to use the image anytime, anywhere in any way they would like.

Bassicly this means you tell them: "Sure, you can use the image in whatever way you like. Anytime, in any resolution/size, any purpose etc. etc.)

One thing to keep in mind with these type of licenses is that (a) you do NOT want them to get the copyright (or local equivalence) on the image and (b) that you should make sure the license does NOT grant them the right to license the image to third partys (essientialy reselling it)

Also if any of the images contain models (NOTE: modeling rights differ quite a lot across country's, in the Netherlands people in your image do share in copyright in certain situations) it might be necessary to you have a license with them as well where they grant you the rights to give these type of licenses (usually you would call this a release, search for "model release" to get a ton of templates). Usually these include what the model is comfortable with and what not when it comes to using the image (I.E. not to be used for commercials for smoking, adult entertainment, certain photoshop editing etc.) If your model release contains these types of restriction, these will of course also have to be in your license to the cliënt. (In Dutch rights (again, this could be different for your situation)) you are liable if you grant your cliënt permission the model has not granted you.

NOTE: this answer in no way covers all the difficult legal stuff. For proper advice contact a lawyer/something. THis is just some things I personally found you should pay special attention to.