Question

define back bonding ???​

Answer 1

π backbonding, also called π backdonation, is a concept from chemistry in which electrons move from an atomic orbital on one atom to an appropriate symmetry antibonding orbital on a π-acceptor ligand. ... Electrons from the metal are used to bond to the ligand, in the process relieving the metal of excess negative charge.

Answer 2

Back bonding:

$\bullet$ It is the donation of electrons.

That is: From the filled atomic orbital of an atom. It provides the lone pair of electrons.

And also,

More number of exchange positions.

$\bullet$ This is called back bonding.

For example: In Borontriflouride, back bonding causes decrease in bond length.

Note: Backbonding is a type of resonance.