The meaning of the term cocrystal is subject of disagreement. One definition states that a cocrystal is a crystalline structure composed of at least two components, where the components may be atoms, ions or molecules. This definition is sometimes extended to specify that the components be solid in their pure forms at ambient conditions. However, it has been argued that this separation based on ambient phase is arbitrary. A more inclusive definition is that cocrystals "consist of two or more components that form a unique crystalline structure having unique properties." Due to variation in the use of the term, structures such as solvates and clathrates may or may not be considered cocrystals in a given situation. The difference between a crystalline salt and a cocrystal lies merely in the transfer of a proton. The transfer of protons from one component to another in a crystal is dependent on the environment. For this reason, crystalline salts and cocrystals may be thought of as two ends of a proton transfer spectrum, where the salt has completed the proton transfer at one end and an absence of proton transfer exists for cocrystals at the other end.