Yoga means concentration of the mind detached from all other subject matter. And actually such concentration is samādhi, or cent percent engagement in the service of the Lord. And one who concentrates his attention in that manner is called a yogī.
-Shrimad Bhagavatam Canto 1 Chapter 9 Verse 23 Purport

यस्यास्ति भक्तिर्भगवत्यकिञ्चना
सर्वैर्गुणैस्तत्र समासते सुरा: ।
हरावभक्तस्य कुतो महद्गुणा
मनोरथेनासति धावतो बहि: ॥ १२ ॥
All the demigods and their exalted qualities, such as religion, knowledge and renunciation, become manifest in the body of one who has developed unalloyed devotion for the Supreme Personality of Godhead, Vāsudeva. On the other hand, a person devoid of devotional service and engaged in material activities has no good qualities. Even if he is adept at the practice of mystic yoga or the honest endeavor of maintaining his family and relatives, he must be driven by his own mental speculations and must engage in the service of the Lord’s external energy. How can there be any good qualities in such a man?
-Shrimad Bhagvatam Canto 5 Chapter 18 Verse 12