Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 3, Verse 2
Pada 3, Sutra 2
Tatra pratyayaika-taanataa dhyaanam
The unbroken flow of attention towards a single point or object is meditation.
Meditation is continuous to concentration. First one needs to withdraw from external distractions occasioned via the propensity of the sense organs by reversing and internalizing their flow. By this economy of sensory motion, one has then the singular opportunity to focus on the object of one’s choice. When this singular focus (i.e. concentration) is uninterrupted it becomes meditation. Only the object is evident (to the exclusion of everything else) in meditation.
Sustained attention is meditation. Awareness must become one-pointed first before it can experience singularity of attention.