Yearly Themes are a powerful concept that I first discovered thanks to CGP Grey. He made a nice video about them and discusses them regularly on Cortex.
Each year, or season, you set a theme that describes a change you want to make in your life or something new you want to explore or reflect on. It's intentionally a loose and opened-ended concept.
You keep your theme in the back of your head for the year, and it nudges you in the right direction for each decision you make.
In 2020, my yearly theme was "Clarity": figuring shit out, understanding what I want, my place in the world, and the motives of people around me.
These days I am thinking about my theme for 2021; I have got some ideas and will discuss this more in my upcoming yearly review.