Yoga Sutras 1.01-1.05
(endless loop*)
Atha yoga anushasanam
Now, after having done prior preparation through life and
other practices, the study and practice of Yoga begins.
Yogash chitta vritti nirodhah
Yoga is the control (nirodhah, regulation, channeling, mastery,
integration, coordination, stilling, quieting, setting aside) of the
modifications (gross and subtle thought patterns) of the mind field.
Tada drashtuh svarupe avasthanam
Then the Seer abides in Itself, resting in its own
True Nature, which is called Self-realization.
Vritti sarupyam itaratra
At other times, when one is not in Self-realization, the Seer appears
to take on the form of the modifications of the mind field,
taking on the identity of those thought patterns.
Vrittayah pancatayah klishta aklishta
 Those gross and subtle thought patterns (vrittis) fall into
five varieties, of which some are colored (klishta)
and others are uncolored (aklishta).

* Sound should be playing in the background of this page.