Dielectric can be insulators?
Dielectric is an insulator. Electric charges does not flow through it (as in a conductor) but cause polarization (not all insulators can be equally polarized using the same electric field) [1].


  ... dielectric is used to indicate the energy storing capacity of the material [1]


The capacitors store energy electrostatically in an electric field [2]. This electric field interacts with atoms:


  Each atom consists of a cloud of negative charge (electrons) bound to and surrounding a positive point charge at its center. In the presence of an electric field the charge cloud is distorted [1]. 


A better understanding about how a capacitor works can be done using a hydraulic model:

"CapacitorHydraulicAnalogyAnimation" by Sbyrnes321 - Own work. Licensed under CC0 via Wikimedia Commons.


  Charge can flow "through" a capacitor even though no individual electron can get from one side to the other [2].




References:


Wikipedia contributors, "Dielectric," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Dielectric&amp;oldid=615594718 (accessed July 12, 2014).
Wikipedia contributors, "Capacitor," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Capacitor&amp;oldid=615866176 (accessed July 12, 2014).