Dharma has originated from root √धृ dhṛ which means to sustain. The qualities which sustain us are named as dharma. In Manusmṛti, Dharma has been defined as patience, forgiveness, control of our mind, to not steal, purity of mind, body and spirit, control of senses, wisdom, knowledge, truthfulness and to be devoid of anger. All these 10 qualities are called dharma.
धृतिः क्षमा दमोऽस्तेयं शौचमिन्द्रियनिग्रहः।
धीर्विद्या सत्यमक्रोधो दशकं धर्मलक्षणम् ।।
dhṛtiḥ kṣamā damoऽsteyaṁ śaucamindriyanigrahaḥ
Dhīrvidyā satyamakrodho daśakaṁ dharmalakṣaṇam
In one sentence Dharma can be defined as –
आत्मनः प्रतिकूलानि परेषां न समाचरेत्
Ātmanaḥ pratikūlāni pareṣāṁ na samācaret which also means “do unto others as you wish to be done by” as also Bible says