The root meaning of both the Hebrew and Greek words for spirit (Hebrew ruach, Greek pneuma) is "air in motion." Thus these terms are also used for breath and wind (e.g., Exodus 15:8 "blast"; Psalms 135:7; John 3:8). The primary idea is that of vitality and power. As such, the term spirit denotes the life principle or force. In calling God "spirit" (or "Spirit," John 4:24), Scripture portrays God as pure living power in contrast to the weakness of that which is material or flesh (cf. the contrast in Isaiah 31:3). Created spirits (including angels), although limited in comparison to God, are still seen as powerful throughout Scripture.
In relation to mankind, the spirit is the principle of life that comes from God to animate the body or flesh (cf. Genesis 2:7, "breath of life"; James 2:26). It is also in this principle of life that the personhood of the human being (i.e., self-consciousness and self-determination) resides, although it is manifest through the body, before physical death. Physical death is the departure of spirit from the body (cf. James 2:26). Separated from the body, the spirit exists in a disembodied state until the resurrection (cf. Hebrews 12:23). As the life force, the spirit manifests itself in various ways depending on the person's (perceived) limitations. It also represents the dominant disposition that controls a person at any given time (e.g., a spirit of grief, a spirit of anger).
Animals likewise have spirit as the animating principle. An animal spirit, however, is of a different quality than a human spirit, not being formed to perceive abstraction (such as good and evil) like a human's (cf. Zechariah 12:1).
This topic is from the Lockman Foundation.