The answer is: the physical reactions you experience during an emotion.
We experience a lot of different emotions throughout our lives and they seem to play a significant role in our everyday lives since we take decisions based on whether we feel happy, angry, sad, bored, or anxious, among others. According to some psychologists our emotions are, in fact, complex psychological states that involves mainly three different elements: a subjective experience, a physiological response, and a behavioral or expressive response.
To begin with, we may identify the subjective experience as the emotions we feel according to our personal experience throughout our lives. As psychological subjects, we may go through different emotions, but our own unique experience is the key to shape the emotions we feel in certain situations. The list of emotions we feel is probably much more varied than you think since we do not always experience pure forms of each emotion in the same way. In other words, in a particular situation, we may experience a combination of different emotions simultaneously. However, this varied list of emotions over different situations is pretty common. For example, if you are about to experience a new event in your life, like starting a new job or college, you might feel both excited and nervous but if you are watching a romantic film, you may feel a wide variety of other emotions that may range from joy to sadness based on your own personal experience about this particular situation.
You may have also realized that certain emotions also trigger strong physiological reactions or body involuntarily movements and this is known as the physiological responses of our bodies. Sweating palms, racing heartbeat, rapid breathing and many other of the diverse physical reactions you may experience during an emotion are mainly controlled by our own nervous system. The nervous system is in charge of the body's reactions during a threat or a dangerous situation. When facing a threat, these responses automatically prepare your body to escape from danger, for instance. Without these spontaneous and random reactions, we would not be able to take the fastest and most convenient responses in case of threat or danger.
Finally, the last element that shape our emotions is the behavioral or expressive response. This response is, in fact, the actual representation of the emotions we feel. More interestingly, we are able to interpret these emotional representations of the people around us and we are also able to understand what they mean in a particular situation. This ability to accurately decode and understand these expressions is related to emotional intelligence we have as the psychological subjects who are immersed within a particular community. Moreover, these expressions play an important role in our overall body language. Many researchers, for instance, claim that many emotional expressions we use in our everyday lives are, in fact, universal: A smile, for instance, that generally indicate happiness in most cultures.