The philosophy of textual interpretation.
Hermeneutics is the overarching term given to theories and methods of interpreting linguistic communication. Questions here regarding hermeneutical approaches ask about these methods or theories as applied to the Bible (and cognate literature).
Some hermeneutical approaches include lexical-syntactical analysis, historical/cultural analysis, contextual analysis, theological analysis, and special literary analysis. Other principles exists such as the principles of innerancy, reverence, and historico-grammatical interpretation.
On this site, "hermeneutics" is somewhat intertwined with "exegesis". See the Q&A on "What is the difference between exegesis and hermeneutics?" for a discussion of differences.