In layman's terms,
self-actualization is when you have reaped the maximum potential out of your personal talents, abilities,
creativities and ambitions.
Self-actualization only happens when all your lower
primal needs have been met (e.g. physiological needs, emotional needs).
While self-actualization initially paints a pretty picture inside your head, do not be fooled as the journey is actually quite excruciating. In order to become fully self-actualized you'd have to push yourself to the limits. You'd have to devote yourself solely towards your ambitions and talents, no slacking or fun and games. The world's biggest entrepreneurs such as Steve Jobs were 100% self-actualized, but boy they were under a lot of stress and often overworked to the core.
In summary, self-actualization is a very good thing, but it's not for the weak-minded.