These type of defects are also called dislocations or line defects (1-D).   They are caused when a portion of the crystal slides or slips relative to another.  the plane in which the dislocation moves through the lattice is called the slip plane.

 The result is a distorted region along a line AB also called the dislocation line. There are three possible cases:

1. atoms are displaced ^ to AB ® edge dislocation

2. atoms are displaced  || to AB  ® screw dislocation

3. atoms are displaced at other angles ® mixed dislocation: