a spirit being, in animal form, which stays with you to teach and protect you
a spiritual entity that provides you with specific spiritual wisdom and medicine
A guide and protector of an individual that resides in the spirit worlds. A Power Animal appears as a specific animal to the individual and is one of their closest allies in life and in spiritual practices. A power animal is not a specific animal, but an archetypal force of all species of that animal. Therefore a power animal won't be a specific fox you saw as a child but is Fox (with a capital F) that embodies the energies and characteristics of all species of fox on Earth.
An animal spirit with special characteristics and attributes that represent traits or qualities you have or need.
A catch-all for New Age spiritualism used as psychology. The actual technique may be fictitious, but has been mentioned in the movies Fight Club and Thumbsucker. According either movie the process involves the exercise of visualizing animals as a source of strength.