Wikipedia
Self-disclosure is a process of communication by which one person reveals information about himself or herself to another. The information can be descriptive or evaluative, and can include thoughts, feelings, aspirations, goals, failures, successes, fears, and dreams, as well as one's likes, dislikes, and favorites.
Social penetration theory posits that there are two dimensions to self-disclosure: breadth and depth. Both are crucial in developing a fully intimate relationship. The range of topics discussed by two individuals is the breadth of disclosure. The degree to which the information revealed is private or personal is the depth of that disclosure. It is easier for breadth to be expanded first in a relationship because of its more accessible features; it consists of outer layers of personality and everyday lives, such as occupations and preferences. Depth is more difficult to reach, and includes painful memories and more unusual traits that we might hesitate to share with others. We reveal ourselves most thoroughly and discuss the widest range of topics with our spouses and loved ones.
Self-disclosure is an important building block for intimacy and cannot be achieved without it. We expect reciprocal and appropriate self-disclosure. Self-disclosure can be assessed by an analysis of cost and rewards which can be further explained by social exchange theory. Most self-disclosure occurs early in relational development, but more intimate self-disclosure occurs later.