The term identity is something that is very complex to understand fully, and has been defined in a number of different ways. Some people use the term to refer to a series of characteristics that helps differentiate a person or a thing from others, referring to unique identity. Others use the term to talk about the quality of being like somebody else or being part of a certain group. However, the enotes page that I have provided the link of below defines identity as follows:
A person's mental representation of who he or she is.
It is important to remember the various different definitions of identity, and also to be aware of the way in which identity is something that is personal but also social. In one sense, identity is about defining yourself compared to others, focusing on how you are unique from them. However, at the same time, we all have social identities that result from our involvement in various groups. These groups can be related to our status in life or occupation, the country in which we live and our class, to name but a few. These group identities can be very useful in helping people to define their identity, both for themselves and for society at large.
Let me give you an example. For me, my identity is shaped by my personal characteristics, which include my love of literature and reading and of culture, walking and exercise. However, equally, my identity is shaped by how I identify myself with certain groups: I am white Englishman, I am a teacher and I am a Christian, and I am also an Editor on Enotes. All of these things help construct my identity. In any definition of identity therefore it is important to remember both the individual aspect of identity that makes you unique, but also the corporate aspect, which identifies how we are similar to others.