Sentence:  When dealing with various <WSD>polynomial bases</WSD> up to a certain degree and with corresponding moments, any moment (with respect to any basis) can be expressed as a function of moments of the same or fewer orders with respect to an arbitrary basis....As we already saw in Chapter 1, OG[orthogonal] moments are, unlike geometric and all other moments, coordinates of f in the <WSD>polynomial basis</WSD> in the common sense used in linear algebra. 
Meaning of the word marked with <WSD> tags:  A basis of a polynomial ring (said ring being viewed either as a vector space over the field of coefficients or as a free module over the ring of coefficients).