Revelation Online Details the Aptitude System
Depending on your level, that Aptitude can then be spent to earn additional experience. Your Aptitude reservoir is limited, so once it fills, a dedicated NPC called Mora Zin will save it all for you, preventing from losing the extra Aptitude. The purpose of this system is that players who are unable to play on a regularly basis to "not miss out on the daily aptitude."
You can read details at the official site.