to over-defend a point e.g. e4 is overprotected with Bc2, Nd2, Re1, Qe2, Ng3. The idea is that after e.g. Nf5 and an exchange ...Bd7xf5, the recapture e4xf5 will suddenly open up lines for the patient White pieces. Nimzovitch seemed to say that overprotection is an end in itself, but more plausible is that over-protection may make a strong move like Nf5 more decisive. There are examples in the strategy/themes section of the Canon.