Today is Thursday. Thursday is today.
Yesterday was Wednesday. Wednesday was yesterday.
Tomorrow is Friday. Friday is tomorrow.
This month is December. December is this month.
Last month was November. November was last month.
Next month is January. January is next month.
This year is 2024. 2024 is this year.
Last year was 2023. 2023 was last year.
Next year is 2025. 2025 is next year.
This decade is the Twenties. The Twenties is this decade.
Last decade was the Teens. The Teens was last decade.
Next decade is the Thirties. The Thirties is next decade.
This century is the 21st. The 21st is this century.
Last century was the 20th. The 20th was last century.
Next century is the 22nd. The 22nd is next century.
Now are you clear about when what is?