Yōga Sūtra 3.03

तदेवार्थमात्रनिर्भासं स्वरूपशून्यमिव समाधिः।

tadēvārthamātranirbhāsaṁ svarūpaśūnyamiva samādhiḥ।

[तदेव अर्थ मात्र निर्भासं स्वरूप शून्यम् इव समाधिः।
tadēva = when that object of meditation; artha = understanding; mātra = only; nirbhāsaṁ = comprehended; svarūpa = form; śūnyam = without; iva = that only; samādhiḥ = is samādhi;]

When that (object of meditation) is comprehended with its understanding only, without form, it is Samādhi.