What is a cluster arpeggio?

[djokluv]

I am to play a commissioned piece for a contest, but I've never seen this before and can't find anything like it online.  Does anyone know how it's played?

[quantum]

From the notation, it looks similar to a rolled chord.  Instead of a chord, it is a palm, fist, forearm, etc. cluster, rolled in the direction of the arrow.  A cluster with fingers is possible too, but not as many keys can fit under the fingers.  If there were no additional directions in the score, that is how I would approach the notation.  The score does say approximate pitch, so there is wiggle room.

Is there any instruction in the score if the composer specifies natural (white keys), sharps (black keys) or chromatic (all keys) clusters?

I would interpret the ties that connect to nothing as to be played laissez vibrer. 

[kosulin]

Cluster means that there are multiple consecutive scale notes played together, for example semitone apart, usually to create a dissonant sound. Popular in modern jazz guitar, but as a chord, not arpeggio.
But I did not see such notation before, in guitar it is just a chord name, or a bold vertical line, not a rectangle. 
I agree with previous comment, the author most likely means the rolling chord made of all notes between the top and lower ones played in the direction of the arrow.
And the words probably mean "cluster arpeggiated", not "arpeggio".

Update: Dolmetsch Online describes this symbol as "cluster white" whatever that means. I do not think it means something different from the the bold vertical line which Dolmetsch names "cluster black".
Update 2: yes, this is a usual cluster (but arpeggiated in the arrow direction), I found such white rectangle in Sibelius.

P.S. Ive never understood why people invent new confusing notation for a well known stuff. In the case of this white rectangle it would be much more intuitive IMHO to connect the top and bottom notes of the cluster with bold black vertical line, a usual cluster notation.

[djokluv]

@quantum: Thanks for your response! No, it doesn't say anything about white / black / chromatic keys.
@kosulin: That's interesting.  When I was looking it up, I did find a lot of topics on it for guitar and non-classical music.  That makes sense.  Thank you.