In the Gītā commentary this means roughly being (bhava) in-accord- ance-with (anu) what truly is. The sense comes out clearly in III.41 and IX.1, where the Gītā has the pair jñāna-vijñāna. (This is translated by Edgerton as theoretical and practical knowledge.) In this pairing, jñāna is taken by Śaṅkara not in the usual way as Right Vision (samyag- darsana), but as theoretical ideas (avabodha) of the Self and so on as taught by scripture and the teacher. Vijñāna in contrast is practical realization of the ideas – anubhava.
Similarly in IX. 1 vijñāna as anubhava is distinguished from jñāna. But he also treats the pair together as samyagdarsana, ‘the direct means to mokṣa.
The three terms – paripāka, avasāna, anubhava – came together (each twice) in XVIII.55. They also appear under XVIII.36 and 37.
The Gītā and Śaṅkara both treat the teaching-point here as most important: Kṛṣṇa introduces it with Hear!, which Śaṅkara glosses as: Be Concentrated (samādhānam kuru).
XVIII.36 Hear from me about the three-fold happiness.
What with practice one delights in, where pain comes to an end,
XVIII.37 Which at the beginning seems like poison but with maturity is like honey
That is said to be the happiness of light (sattva),
Arising from the peace of a mind-resting-on-Self (ātmabuddhi).
‘with practice’ means by application and facility; ‘delight’ means happi- ness-realization (sukha-anubhava). He does not use anubhava for the momentary experience of false happiness of excitement or the deluded happiness of sloth.
Śaṅkara explains that at the beginning, when jñāna, vairāgya, dhyāna and samādhi are first tackled head-on, they are nothing but effort; in this preliminary stage, they seem against natural well-being – poison as it were. But when the jñāna, vairāgya, dhyāna and samādhi are mature (paripāka) the happiness is comparable to honey of immortality.