1 At its most general, a quality or even a virtue. This sense is perhaps related to the more specific Nyāya-Vaiśeṣika view of guṇas as the perceivable attributes which indicate the existence of a substance (dravya). Lists of such qualities most commonly include those available to the senses (taste, touch, colour, etc.), and the mind (cognition, volition, attraction, etc.).
2 According to Sāṃkhya-Yoga ontology, the (tri)guṇas are the three inextricably intertwined strands, or constituents, of material nature (prakṛti), the dynamic interaction of which constitutes the physical universe—i.e. everything except the non-material ‘persons’ or puruṣas. For purposes of analysis, the guṇas are separated into pure (sattva), passionate (rajas), and dark (tamas) strands—the sattva guṇa representing the principle of pure thought, the rajas guṇa that of kinesis, and the tamas guṇa that of inertia. Prior to the evolution of the universe, these three guṇas exist in a state of perfect equilibrium or unmanifest potentiality (pradhāna); but once their balance is upset by the influence of puruṣa, they manifest themselves in the evolutes, which make up the variegated world. Thereafter, it is the predominance, or otherwise, of particular guṇas in material nature (including the mind) which constrains beings to act in particular ways.
Versions of this understanding of the guṇas can be found across a significant number of Indian religious and philosophical systems, often tailored to particular ends. So the Bhagavadgītā, for instance, which is more concerned with the transformation of already embodied individuals than with the evolution of the universe per se, associates the sattva guṇa with knowledge and freedom from pollution, the rajas guṇa with activity, energy, and greed, and the tamas guṇa with inertia and ignorance; but ultimately it subsumes all three within God's (Kṛṣṇa's) lower nature.