The word "flex" mainly means to bend or to move something, usually referring to muscles or objects. In a more colloquial sense, it can also imply showing off or displaying something, often in a boastful manner. For instance, when someone "flexes" their muscles, they are demonstrating their strength, and when someone "flexes" their wealth, they are showcasing their financial success.
The term "flex" comes from the Latin word "flectere," which means "to bend." It has been used in English since the early 15th century and has evolved to include both literal and figurative meanings.