I am not a pure Statistics background and therefore please forgive me if
this question (which is not R related either) is too trivial.

In many Statistics literature I find following statement: "restrictions in
different coefficients matrices have to be imposed to ensure uniqueness of
the parametrization". Can somebody tell me what is the meaning of Uniqueness
in the parametrization? Does it mean that, two different coefficient
matrices may give exactly the same result, and therefore coefficient matrix
is not unique?

I find there are many members (perhaps all) in this forum who are really
masters in Statistics. Therefore I hope somebody will clarify me with the
intuition behind that.

Thanks,

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