A generic name for carbocations, real or hypothetical, that have at least one important contributing structure containing a tervalent carbon atom with a vacant p-orbital. (The name implies a protonated carbene or a substitution derivative thereof.) The term was proposed (and rejected) as a replacement for the traditional usage of the name carbonium ion. To avoid ambiguity, the name should not be used as the root for the systematic nomenclature of carbocations. The corresponding difficulty confused carbonium ion nomenclature for many years. For example, the term 'ethylcarbonium ion' has at times been used to refer either to CH₃CH₂⁺ (ethyl cation) or (correctly) to CH₃CH₂CH₂⁺ (propyl cation).