[Jakov_the_Jakovasaur]

in addition to what cyan3 said, classes are not an actual object such as an npc or weapon, but scripts which are essentially copied and pasted (dynamically) into other scripts. you can join multiple classes into one script, you can join classes within classes, and classes can be joined to multiple different types of objects which for example includes players

npcs within rc (often called database npcs) are permanent objects which are not binded to a particular level, so for example if you updated a level all npcs within it would reset to their original state whereas a database npc would retain variables which were stored on it. database npcs can also be warped into different levels and can have their scripts processed without players being in the same level