What situation is referred to as shielding?

Question

Question Quiz SPL - Sailplane Pilot License - Meteorology

QuizVDS · Accepted Answer

High or mid-level cloud layers, impairing thermal activity

QuizVDS · Answer

Ns clouds, covering the windward side of a mountain range

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Anvil-like structure at the upper levels of a thunderstorm cloud

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Coverage of Cumulus clouds, stated as part of eights of the sky

Id 303 - SPL - What situation is referred to as "shielding"?