'sticky' ends

 Also known as cohesive ends, sticky ends are formed when a double stranded DNA fragment is asymmetrically cleaved by certain restriction enzymes such as EcoRI. These ends will be complementary to each other so once paired two DNA fragments can be joined together permanently by DNA ligase which catalyses the formation of bonds between the sugar-phosphate groups between the fragments.

This technique is often used in recombinant DNA technology.