What is Existentialism?

What is Existentialism?
"Existentialism is a term applied to the work of a number of 19th- and 20th-century philosophers who, despite profound doctrinal differences, generally held that the focus of philosophical thought should be to deal with the conditions of existence of the individual person and his or her emotions, actions, responsibilities, and thoughts."
(via wikipedia )

Simpler enough, existentialism is a philosophical idea and movement which states that "existence precedes essence" (Sartre). This places man in control of his own destiny and strips him bare of any preconceived human nature (essence). Every man has the power within himself to construct his own identity and his own way of being in the world (good faith). For this reason, existentialism places humanity at the center of its philosophical spectrum, which includes first and foremost the importance of human subjectivity (self-consciousness).