dhyanaheyah tadvrttayah yogic sutra delineates about the waverings that one faces while meditating or pondering. These are generally induced by the subtle adversities, that too of severe intensities. Profound meditation is a means of curbing these diversions of thoughts.

dhyana meditation, reflection, attention, observation
heyah annihilated, rejected, quietened, avoided, silenced
tad their
vrttayah fluctuations, movements, operations

The fluctuations of consciousness created by gross and subtle afflictions are to be silenced through meditation.

This is a way to point towards a way of checking the modifications of thought-waves. In 10th yogic sutra, the mind is silenced through involution, the practice of renunciation or folding-in of the mind. Here, Patanjali offers meditation as another method to calm the mind. By these means, the mind`s whims are reduced to their subtlest point and it is constrained to rest silently in its source, the soul.

Afflictions are of three intensities - gross (sthula), subtle (suksma), and the subtlest of the subtle (suksmatama). Tapas, svadhyaya and Iivara pranidhana exterminate the gross, the subtle and the subtlest afflictions respectively.