Re: equlisers...
There is no fundamental difference.
I suppose the term equalizer traditionally means "making frequencies equal." In order to estimate a distorted signal, that is exactly what you have to do. On the other hand, the term is now also being used in the context of non-stationary signals, where a frequency domain interpretation is not strictly possible.
So I'd say the two mean the same thing, but the term equalizer is commonly used in signal processing, while the term estimator is more general.