Typically the lump many refer to is where your7th cervical vertebrae sticks out.  It has a slightly longer spinous process back of the vertebrae) to be gin with but then we add forwad head posture to the equation and it appears more protruded.  Over time we start to get hunching of the upper thoracic spine.  When this gets irritated you can get some local pain and even inflammation.  Neck exercises such as head retractions can help.

http://www.neckpainreliefkit.com/neckexercises