You and I call it ISIS. Obama calls it ISIL, and Kerry calls it Daesh, D-a-e-s-h, because that's the term the French like. I'm not making that up. Daesh is the term that the French like, so that's what Kerry uses, and because it's, in his mind, much more sophisticated to use the term Daesh. It also conveys more respect for the group than to simply call them the derisional ISIS.
I have a slightly different interpretation of Kerry's use of Daesh. Kerry intends to confuse the public as to who the Islamic State is and what the group wants. George Orwell's essay "Politics and the English Language" advised against using foreign terms were an English equivalent is available. When I refer to Islamic State, I always use the words "Islamic State". It is a simple English term that accurately describes who the group is ("Islamic") and the group's ultimate goal (setting up an Islamic "State").
I avoid the use of ISIS or ISIL because those abbreviations hide the Islamic nature of the organization and don't provide insight into the group's goal. My understanding is that Daesh is an Arabic contraction of some sort. Why use an Arabic contraction? American's don't know the meaning of the Arabic words used in the contraction, and the contraction necessarily loses a little meaning (just like using ISIS or ISIL does).
George Orwell in Politics and the English Language:Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent
When I hear isis I think insane, murderous mooselimb
When I hear isil I think insane, murderous mooselimb
When I hear daesh I think insane, murderous mooselimb
When I hear islam I think insane, murderous mooselimb
When I hear sunni I think insane, murderous mooselimb
When I hear shiit I think insane, murderous mooselimb
When I hear al quaeda I think insane, murderous mooselimb
When I hear hezbollah I think insane, murderous mooselimb
When I hear hammas I think insane, murderous mooselimb
When I hear mosque I think collection of insane, murderous mooselimbs
It’s really quite simple and I don’t have to know Arabic.