Laith Al-Shawaf in Psychology Today:
Emotions are crucial to our lives, so you might be surprised to hear that psychologists don’t have a consensus definition of what they are or how they work.
Despite the chorus of different voices, there are some things emotion scientists agree on. Most researchers agree, for example, that all emotions have a physiological component, a phenomenological component (what it feels like to experience that emotion), and a behavioral component (for instance, some emotions prime you to fight, whereas others make you more likely to play).
There’s a prominent evolutionary view that expands on this idea. According to this view, an emotion is a coordinating mechanism or a “mode of operation” for the entire body and brain. In other words, when an emotion like fear takes hold, it affects everything in your body and mind: it influences what you can see, what you are able to focus on, what is readily available to your memory, where metabolic resources are distributed in your body, the manner in which you categorize objects as safe or dangerous, how you prioritize your goals, and pretty much everything else about the way you parse the world.
More here.