Dharma, generally it is understood "religion." Religion means a kind of faith. So that is not the proper meaning of dharma, "faith." Faith one may have, one may not have. But actually dharma means compulsory. It must be. Just like sugar. Sugar must be sweet. There is no question of sometimes becoming sweet and sometimes becoming bitter. That is not sugar. Sugar must be sweet. Similarly, dharma is also a "must be." It cannot be option or a kind of faith which you can change at your whims. That is not dharma. Dharma means "must be." The same example: A particular thing has a particular characteristic. The sugar characteristic is sweetness. Chili is hot. Similarly, everything has got its characteristic. Just like microphone. I am speaking; it must resound. That is the characteristic. That is dharma, which cannot be separated. If sweetness is separated from sugar, it is no longer sugar. Similarly, dharma means that. Dharma means, real meaning is, characteristic.
The characteristic of the living being is to serve. Caitanya Mahāprabhu gave this instruction. Jīvera svarūpa haya nitya kṛṣṇa dāsa [Cc. Madhya 20.108-109]. That is the characteristic of all living entities, to become servant, to become servant of Kṛṣṇa. But when we do not serve Kṛṣṇa, then, because my constitutional position is to serve, I have to serve māyā. If you don't serve Kṛṣṇa, then you will have to serve māyā. Because you have no other business than to serve. Just like a servant class. If he gives up one master, he must accept another master. May be better master, but master he has to accept. Just like dog. Without accepting a master, it is street dog. It has no position. So dharma means that, the characteristic of the living being.
Prabhupada's lecture - Śrīmad-Bhāgavatam 1.2.9 - Detroit, August 3, 1975, University Lecture