ozone layer
This term refers specifically to the atmospheric shield protecting Earth from ultraviolet radiation. It is almost exclusively used in scientific, environmental, and educational contexts, carrying a strong connotation of fragility and ecological urgency due to the historical focus on its depletion.
Grammatically, while the word "layer" is typically countable, "ozone layer" is treated as a unique geographical and atmospheric entity. It is almost always used in the singular because Earth possesses only one such global system, making plural usage extremely rare and typically incorrect in a standard scientific context.
Meanings
A region of Earth's stratosphere that contains a high concentration of ozone molecules, which absorbs most of the sun's harmful ultraviolet radiation.
The depletion of the ozone layer is a major environmental concern.