In econometric theory two possibie situations of identifiability can arise: Equation under,consideration is identified or not identified:
1) Equation is under-identified-
If the structure of the equation is not unique or there is not sufficient linformationtto uniquely disfinguish the equation then the equation is under- identified.
2) Equation is identified
(a) Exactly identified: If there is sufficient information available to distinguish the equation then it is called just identified or exactly identified equation
(b) Over identified: If there is more than sufficient information regarding the equation then th$ equation is called over-identified.