Question

what is the main difference between (bridging ligand-''Mu'') and (hapticity-"eta")

Answer 1

bridging ligand-''Mu''

In coordination chemistry a bridging ligand is a ligand that connects two or more atoms, usually metal ions.

example of bridging ligand

OH−

hydroxide

[Fe2(OH)2(H2O)8]4+

so here L  μ² bridging ligand

hapticity-"eta"

Hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms.

example of heptacity eta is  

Ferrocene - bis(η⁵-cyclopentadienyl)iron

Ferrocenecontains two η⁵-cyclopentadienylligand.

The source of information is wikipedia.