What is the name of "cis/trans" isomerism when all four groups are different?
When all four substituents are different cis-trans type of isomerism cannot be applied.  Moreover the Cis trans system is often ambiguous because configurational descriptions have not been defined according to any general and clear set of rules. For these types,  there is system called E-Z system of nomenclature and is based on the sequence rules of Cahn, Ingold  and Prelog (CIP) rule, originally developed for naming optical isomers on R-S system