the phenomenon of not permitting the passage of electromagnetic radiation
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incomprehensibility resulting from obscurity of meaning
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the quality of being opaque to a degree; the degree to which something reduces the passage of light
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Opacity \O*pac"i*ty\, n. [L. opacitas: cf. F. opacit['e].] 1. The state of being opaque; the quality of a body which renders it impervious to the rays of light; want of transparency; opaqueness.
2. Obscurity; want of clearness. --Bp. Hall.
In essence, the debate centers around the so-called "opacity standard" developed by the state.