An edge
dislocation is a fault in a
crystalline structure. Imagine a
deck of cards. If you took the card off of the top and slid it into the middle of the deck like so:
------------- < - - - top card
-------------
-------------
|-------------
-------------
-------------
------------- < - - - bottom card
The end of the card sticking into the deck would be the edge dislocation. The edge is dislocated from its proper place at the left side of the deck.
This dislocation causes problems with the crystalline lattice. It stretches the lattice apart where it is intercalated, and causes compressive stresses there. The part of the lattice in which it is absent is placed under tensile stresses. These stresses (and their resultant strains) move the atoms in the lattice from their lowest-energy spots in their potential wells to higher energy spots, thus raising the potential energy of the lattice overall. Interstingly interstitial impurity atoms can wedge into the larger or smaller space produced by these strains, alleviating some of the forces. Larger particles will tend to fit into the areas between atoms in tension, and smaller ones between those in compression.
The dislocation is indicated schematically by a line perpendicular to the inserted card at the edge. It can be seen in the above diagram. It is called the dislocation line and moves in the slip plane, which is parallel to itself and perpendicular to the inserted plane.
Like screw dislocations and mixed dislocations, edge dislocations have an associated Burgers Vector.
This information was derived from my Materials Science and Engineering lecture notes.