cordiante bond

COORDINATE COVALENT BOND
The type of chemical bond in which one atom provides shared pair of electron for bond formation is called "Coordinate Covalent Bond".
OR
Chemical bond formed between two atoms due to sharing of electron pair in which only one atom provides shared pair of electron for the formation of bond, is known as coordinate covalent bond or dative bond.
In the formation of coordinate bond other atom does not provide electron for sharing. It is one sided sharing. Formation of coordinate covalent bond is the property of atoms that have lone pair of electrons.
The atom that provides electron pair is called "Donor".The other which takes it is called "Acceptor".
Symbol: Dative bond is represented by an arrow (®), pointing from donor atom to the acceptor.
www.citycollegiate.com
Examples: Ammonium ion Hydronium ion