Definition of Yoga

As Per Patanjali

योगश्चित्तवृत्तिनिरोधः

Yoga Chitta Vritti Nirodhah

Yoga is the cessation of fluctuation of the mind.

As Per Bhagwad Gita

योग: कर्मसु कौशलम्

Yogaḥ Karmasu Kauśhalam.

Yoga is Skills/ dexterity in action.

समत्वं योग उच्यते।

Samatvam Yoga Ucyate

Yoga is equanimity of mind

As per Katho Upanishad

स्थिरामिन्द्रियधारणाम्

Sthirām indriya dhāraṇām

Yoga is a state where our Indriyas are beheld steadily