Ligands are ions or molecules bound to the central atom/ion in a coordination entity. They can be simple ions like Cl⁻, small molecules like H₂O or NH₃, or even larger molecules such as proteins. Examples include Cl⁻, H₂O, NH₃, H₂NCH₂CH₂NH₂, ...

The central atom/ion is the one to which a fixed number of ions/groups are bound in a definite geometric arrangement. Examples are Ni²⁺ in [NiCl₂(H₂O)₄], Co³⁺ in [CoCl(NH₃)₅]²⁺, and Fe³⁺ in [Fe(CN)₆]³⁻, also referred to as Lewis acids.

A coordination entity consists of a central metal atom or ion bonded to a fixed number of ions or molecules. Examples include [CoCl₃(NH₃)₃], [Ni(CO)₄], [PtCl₂(NH₃)₂], [Fe(CN)₆]⁴⁻, and [Co(NH₃)₆]³⁺.

Double salts dissociate into simple ions when dissolved, whereas complex ions, like [Fe(CN)₆]⁴⁻ in K₄[Fe(CN)₆], do not dissociate into their constituent ions, maintaining their structural integrity in solution.

Numerical prefixes like mono, di, tri indicate the number of ligands. Terms like bis, tris, tetrakis are used when ligand names include numerical prefixes, placed in parentheses. For example, [NiCl₂(PPh₃)₂] is named dichloridobis(triphenylphosphine)nickel(II).