You do a lot of tasks, oftentimes it so happens that you have a strong desire to do a certain thing. That desire could be the simple term used for motivation. Self-Motivation in that sense is just the desire you could create on your own.
Motivation is like fuel, which drives you towards getting what you want through the task at hand. The level of motivation has the capacity to surpass the percentage of success probability or danger involved.
And self-motivation is the ability to regenerate the energy in your journey to success.