Motivation that comes from within a person, rather than an external source. Often people likes to label others as either motivated or not, while I believe that self motivation and external motivation are entirely distinct. Some respond better to external motivators like school or money while others would continue with an activity if they were the last person on earth.
People who are externally motivated, say by peer respect or status might not be able to find the will to do something that will not bring an external reward. Often people with high levels of self motivation, such as obsessive Hackers, Writers and musicians are seen as lacking motivation when they seem disinterested in seeking to increase their social standing.
Examples of activities that generally may require self motivation:
Reading books independent of work/class requirements.
Starting an exercise program.
Learning to play a musical Instrument.