Bg 6.18

yada viniyatam cittam
atmany evavatisthate
nisprhah sarva-kamebhyo
yukta ity ucyate tada

Word for word: 
yada — when; viniyatam — particularly disciplined; cittam — the mind and its activities; atmani — in the transcendence; eva — certainly; avatisthate — becomes situated; nisprhah — devoid of desire; sarva — for all kinds of; kamebhyah — material sense gratification; yuktah — well situated in yoga; iti — thus; ucyate — is said to be; tada — at that time.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When the yogi, by practice of yoga, disciplines his mental activities and becomes situated in transcendence – devoid of all material desires – he is said to be well established in yoga.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The activities of the yogi are distinguished from those of an ordinary person by his characteristic cessation from all kinds of material desires – of which sex is the chief. A perfect yogi is so well disciplined in the activities of the mind that he can no longer be disturbed by any kind of material desire. This perfectional stage can automatically be attained by persons in Krishna consciousness, as stated in the Srimad-Bhagavatam (9.4.18–20):

sa vai manah Krishna-padaravindayor
vacamsi vaikuntha-gunanuvarnane
karau harer mandira-marjanadisu
srutim cakaracyuta-sat-kathodaye

mukunda-lingalaya-darsane drsau
tad-bhrtya-gatra-sparse ’nga-sangamam
ghranam ca tat-pada-saroja-saurabhe
srimat-tulasya rasanam tad-arpite

padau hareh ksetra-padanusarpane
siro hrsikesa-padabhivandane
kamam ca dasye na tu kama-kamyaya
yathottama-sloka-janasraya ratih

“King Ambarisa first of all engaged his mind on the lotus feet of Lord Krishna; then, one after another, he engaged his words in describing the transcendental qualities of the Lord, his hands in mopping the temple of the Lord, his ears in hearing of the activities of the Lord, his eyes in seeing the transcendental forms of the Lord, his body in touching the bodies of the devotees, his sense of smell in smelling the scents of the lotus flowers offered to the Lord, his tongue in tasting the tulasi leaf offered at the lotus feet of the Lord, his legs in going to places of pilgrimage and the temple of the Lord, his head in offering obeisances unto the Lord, and his desires in executing the mission of the Lord. All these transcendental activities are quite befitting a pure devotee.”

This transcendental stage may be inexpressible subjectively by the followers of the impersonalist path, but it becomes very easy and practical for a person in Krishna consciousness, as is apparent in the above description of the engagements of Maharaja Ambarisa. Unless the mind is fixed on the lotus feet of the Lord by constant remembrance, such transcendental engagements are not practical. In the devotional service of the Lord, therefore, these prescribed activities are called arcana, or engaging all the senses in the service of the Lord. The senses and the mind require engagements. Simple abnegation is not practical. Therefore, for people in general – especially those who are not in the renounced order of life – transcendental engagement of the senses and the mind as described above is the perfect process for transcendental achievement, which is called yukta in the Bhagavad-gita.