CPU_NinjaStars

Can someone explain what the difference between [Tekkit], [Tekkit Light] and [Tekkit Classic] are? I have been searching online only to come up with whats diff. between [Tekkit Light] and [Tekkit Classic] so i understand what differentiates those 2 but i havent been able to come up with much of anything regarding [Tekkit]. Im sorry if this is a stupid question or the answer is out there i did do some searching around but no go.. Thanks in advance!