Core strength refers to the muscles of your abdominal region and your back and their ability to support your spine and keep your body stable and balanced.  The major muscles of your core include transverse, rectus abdominis, external and internal obliques, and erector spinae.  Low back pain is an extremely common result of a lack in core strength, and can be diminished by improving your core fitness and practicing good posture.  When working on your fitness it is important to strengthen the whole body as a unit rather than isolating smaller muscle groups.  For instance, just working your abs, biceps, or legs.  This is a common mistake of many exercisers looking to just improve body  image.  Enhancing athletic performance must include core strengthening since the muscles of the trunk and torso stabilize the spine and allow the transfer of powerful movements of the arms and legs.  Realizing the importance of core strength and practicing fitness exercises focused on building core strength will positively change your body and mind to become more fit and healthy, working in harmony, and thus improving your overall quality of life.