Philosophy is concerned with the pursuit of wisdom: not only with what we think we know, but how? why? and what is it really worth? In line with this spirit of questioning philosophy can be defined as the discipline of critical scrutiny, though its specific methods are informed by a variety of philosophical styles, claims, histories, and concerns from Plato to Kant to Foucault, which constitute often quite divergent schools. Philosophers from different traditions see philosophy differently (check out the anthology of answers by contemporary philosophers to the what is philosophy question over at the excellent Philosophy Bites). But here's my take on it.