In coordination chemistry, hapticity is the coordination of a ligand to a metal center via an uninterrupted and contiguous series of atoms. The hapticity of a ligand is described with the Greek letter η (eta).  For example, η describes a ligand that coordinates through 2 contiguous atoms. In general the η-notation only applies when multiple atoms are coordinated (otherwise the κ-notation is used).  In addition, if the ligand coordinates through multiple atoms that are  contiguous then this is considered denticity (not hapticity), and the κ-notation is used once again.  When naming complexes care should be taken not to confuse η with μ (mu), which relates to bridging ligands.