One of the most versatile words in Japanese is the word 気（き・ki）which can roughly be translated to mean “mind”, “soul”, or “mood”, amongst other definitions. It is derived from the Chinese word Qi, which you may be familiar with as the energy that is traditionally considered to flow through all living things.
Over the centuries, 気 has worked itself into dozens of expressions with various meanings, to the point where it can arguably be considered part of the grammar of the language itself. As a result, it is almost impossible to speak Japanese without understanding the word 気. Here is a brief introduction to 5 of its most common uses.