What is the $\langle \cdot, \cdot \rangle$ operator when calculating Stiefel-Whitney numbers?

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I've been trying to understand Stiefel-Whitney numbers and I'm reading this paper. On page 9, the author defines the Stiefel-Whitney number using an operator $\langle \cdot, \cdot \rangle$. I've tried to look in other places too, but I can't see it defined anywhere. There is an answer here but it seems to boil down to "it is the evaluation map" and I'm not sure what htat means. Can someone help me with a direct definition/formula for this (even in just the case of CW-complexes)?