Financial economics is the branch of economics characterized by a "concentration on monetary activities", in which "money of one type or another is likely to appear on both sides of a trade". Its concern is thus the interrelation of financial variables, such as prices, interest rates and shares, as opposed to those concerning the real economy. It has two main areas of focus: asset pricing (or "investment theory") and corporate finance; the first being the perspective of providers of capital, i.e. investors, and the second of users of capital.
Economics is a subject that really relates to core aspects of human well-being, and there’s a methodology for thinking about these things. This was a very appealing combination to me. Market systems are capable of massive breakdowns that can result in long, devastating periods of high unemployment. And I felt that economists had really learned something about how to address that.
Janet Yellen, in "The Hand on the Lever" in The New Yorker (July 21, 2014) by Nicholas Lemann