Question

animals and plants whose numbers are diminishing to a level that they might face extinction are termed as

Answer 1

hey mate
those animal would be considered as Distinct species

Answer 2

Threatened species are animals and plants whose numbers are diminishing to a level that they might face extinction.  

Explanation:

This can happen due to the increase in population, and the changes made in their environment.  The species depend upon their habitat in which the people bring in changes like cutting down the trees for their own benefits and making those species homeless.

To protect this threatened species, the "International Union for Conservation of Nature" works who involves in gathering information about this and compiling them as "IUCN Red List of Threatened Species". This was invented for global conservation and to provide information about to extinct is of  1000 species.  

For Example: Polar bear.