Attraction is the process by which a relative pronoun takes on -- that is, is "attracted to" -- the case of its antecedent, rather than having the case appropriate to its function in the relative clause. For example, in this English sentence, the relative pronoun has the appropriate case, namely, the accusative:

This is the boss of the man whom I met yesterday.

This sentence, on the other hand, shows attraction:

This is the boss of the man whose I met yesterday.

Because the antecedent, "[of] the man", is possessive, the relative pronoun has become possessive too. Attraction is a theoretical process in standard English, but is common in the Greek of the Septuagint and also occurs in the New Testament.