linear, quadratic and cubic equations

I am studying computer science and have been covering linear, quadratic and cubic algorithms. I am confused as to the difference between them. Can someone explain what they mean in layman's terms?

Maybe even relate to physical objects? One possible example being that a cubic equation relates to three dimensions of something - so what does that mean in real terms that a computer has to go through (presumably in a linear fashion to compute the item) to come to a solution?

Make any sense?