Step 1: Define extinction.
Extinction is when a whole species dies out completely, so that not a single member of it is left anywhere on Earth.
Step 2: Define biodiversity.
Biodiversity is the variety of all the different living species on the planet.
Step 3: Connect the two ideas.
Every time a species goes extinct, the number of species falls, so the variety of life shrinks.
Step 4: Check the other options.
Air pollution, climate change and waste production are environmental problems, but they describe the surroundings, not the loss of species itself.
Step 5: Pick the closest match.
The direct result of extinction is fewer species, which is exactly biodiversity depletion.
Step 6: Conclusion.
The term extinction is mostly related to biodiversity depletion.
\[ \boxed{\text{Biodiversity depletion}} \]