The possible experiences which can be undergone through a meditation practice are highly varied with many contrasting features. Meditation was developed in the Vedic period, which is prehistory, and I'm certain there are all sorts of things which arise, persist, and decline in that human history. Calling this or that state "jhana" is of course the problem; no one disagrees that jhana can
be experienced, but of course the description defines a subtle variety among the multiple possible outcomes of meditation.
The Buddha wanted us to know that his commonest meditative abode was anapanasati, I suspect on account of there being numerous meditative techniques on hand. Further, anapanasati is wholly adequate to the attainment of jhana; other meditative techniques are a potentially distracting à la carte menu. (The exceptions seem to be the Brahmaviharas and kayagatasati - but the Brahmaviharas are the 'Way to heaven', not therefore necessarily capable of fulfilling all four aspects of sammasamadhi, and after the dozens of suiciding monks on the occasion of a discourse on the foulness of the body, anapanasati appears to predominate.)
Therefore, as a preliminary step I'm inclined to discard all meditative experiences which arise outside of anapanasati; such experiences are too loaded with the risk of not being Right Concentration for them to be pursued.
As for an appropriate definition of the jhanas (and therefore of sammasamadhi), I refer to the Maggavibhanga Sutta (SN 45.8
And what, monks, is right concentration? (i) There is the case where a monk — quite withdrawn from sensuality, withdrawn from unskillful (mental) qualities — enters & remains in the first jhana: rapture & pleasure born from withdrawal, accompanied by directed thought & evaluation. (ii) With the stilling of directed thoughts & evaluations, he enters & remains in the second jhana: rapture & pleasure born of concentration, unification of awareness free from directed thought & evaluation — internal assurance. (iii) With the fading of rapture, he remains equanimous, mindful, & alert, and senses pleasure with the body. He enters & remains in the third jhana, of which the Noble Ones declare, 'Equanimous & mindful, he has a pleasant abiding.' (iv) With the abandoning of pleasure & pain — as with the earlier disappearance of elation & distress — he enters & remains in the fourth jhana: purity of equanimity & mindfulness, neither pleasure nor pain. This, monks, is called right concentration.
Four jhana states, and their description. At this point it seems some in-depth Pali studies are in order:
From Tipitaka (Roman)\suttapitaka\samyutta nikaya\mahavaggapali\8. Vibhaṅgasuttaṃ
Katamo ca, bhikkhave, sammāsamādhi? Idha, bhikkhave, bhikkhu vivicceva kāmehi vivicca akusalehi dhammehi savitakkaṃ savicāraṃ vivekajaṃ pītisukhaṃ paṭhamaṃ jhānaṃ upasampajja viharati. Vitakkavicārānaṃ vūpasamā ajjhattaṃ sampasādanaṃ cetaso ekodibhāvaṃ avitakkaṃ avicāraṃ samādhijaṃ pītisukhaṃ dutiyaṃ jhānaṃ upasampajja viharati. Pītiyā ca virāgā upekkhako ca viharati sato ca sampajāno, sukhañca kāyena paṭisaṃvedeti, yaṃ taṃ ariyā ācikkhanti – ‘upekkhako satimā sukhavihārī’ti tatiyaṃ jhānaṃ upasampajja viharati. Sukhassa ca pahānā dukkhassa ca pahānā pubbeva somanassadomanassānaṃ atthaṅgamā adukkhamasukhaṃ upekkhāsatipārisuddhiṃ catutthaṃ jhānaṃ upasampajja viharati – ayaṃ vuccati, bhikkhave, sammāsamādhī’’ti. Aṭṭhamaṃ.
Which words here are the ones of note in the English? In my opinion, this is the only solid place to begin.