Theory is the process of abstraction and rational contemplation of ideas. In simple terms, it can be see as "thinking about thinking".
Theory in a philosophical sense does not require empirical data to support their premises and conclusions. Theory in a scientific sense does require empirical data.
In analytic philosophy, theory is reserved for systematic attempts to solve problems or answer a question  However, non-analytic philosophy can also be referred to any solution to a problem.
Examples of theory:
- Ethical theory are positions taken about the nature of ethical statements 
- Political theory are positions that ground and support a larger political ideology. See John Rawls as an example of this.
- Sparkes, A.W. (1991). Talking Philosophy: a wordbook. New York, New York: Routledge. p. 114. ISBN 0-415-04222-4.
- Richard T. Garner and Bernard Rosen, Moral Philosophy: A Systematic Introduction to Normative Ethics and Meta-ethics. (Macmillan, 1967)