The dictionary defines an icon as "a sign or representation that stands for its object by virtueof a resemblance or analogy to it." So really and icon can be anything that relates to or is similar to something else in any way. I would say that in art there are two types of icons, personal and communal. There are certain icons or symbols that everyone one in our culture understands to represent a certain thing. It could possibly have a different meaning in a different culture. But, as an example, an apple in our culture often represents something forbidden. But in another culture it could represent something entirely different. These culturally understood icons are communal icons. Personal icons would be those objects or symbols that are related to something personal and that would not necessarily be understood by the public as a whole. For example, i might use a certain object in a piece of art that represents a memory that I have.
There are different ways that i have used icons in my own work. One way is that i often use images of women in my collages. In different collages the images of the women represent different things. Sometimes they represent a general femininity, other times they represent idolized beauty, or birth, or oppression. The other images or icons that I use along with the women also changes what they represent. I think that the use of certain colors can also be iconic. Color is something I also think about a lot in my pieces.