= Solution
The <Poynting vector> is the local <electromagnetic energy> flux density:
$$
\boxed{\mathbf N=\mathbf E\times\mathbf H.}
$$
Here $\mathbf E$ is the <electric field> and $\mathbf H$ the <magnetic field intensity>. For an oriented area element $d\mathbf S$, $\mathbf N\cdot d\mathbf S$ is the electromagnetic <power> crossing that element in its positive normal direction. Thus $\int_S\mathbf N\cdot d\mathbf S$ is outward <power> through a closed <surface>, in watts. The <Poynting vector> has units $\mathrm{W\,m^{-2}}$, and its direction describes local <electromagnetic energy> transport.
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