A decade is a period of 10 years. The period of ten years whose numbers begin with 200X is ending, and since that's how we refer to decades (as in 'the 90s'), w

A decade is a period of 10 years. The period of ten years whose numbers begin with 200X is ending, and since that's how we refer to decades (as in 'the 90s'), we say the decade is ending.