It is a combination of two words, Elastic and Polymer. It is a Polymer that displays rubber-like elesticity. The cross linking of the fibers allows for the material to flex without breaking its bond.
You can use a rope as an example of the cross linking. If you grab a rope on bunch it together like a ball it resembles an elastomer at its unstretched state. If you crab a fist full on each side of the rope ball and pull apart will be able to stretch it to a certain extend.
These are great for sealing cracks in the concrete which are prone to movement or control joints that are design to crack if needed. These are not recommended to fill voids or divets in the concrete.