The ‘Day 1’ definiton of Yoga as Union is something most yoga practitioners are given as a standard lecture – both in their teacher trainings as well as in their studio practice at times. Beyond that, if prodded to explain, they describe it with their own imaginative description of defining yoga with various forms of unifying adjectives and adverbs – union of mind, body and breath (though they often get stumped if you asking them what that looked like in practice or if their teacher has demonstrated that to them… ever!?)… They’re right in getting flummoxed, though, as novices, this philosophy is deep work – and steeped in many centuries of tapas and sadhana. So a simple word translated to union doesn’t always get the essence of the practice out to the new aspirant.
But, on a mystic, philosophical lead, after studying various scriptures and listening to various teachers speak on the darshanas as the various commentaries of discourse, there seems to be a common reason to accept that in it’s most basic essence, there is a union involved – and that seems to be elusive as a practical experience.
In short, although yoga is spiritual pursuit, there is much of yoga to experience in the physical and tangible realms too. The experience of connecting our body with our environment – in communion with nature – begins at the gross level, the annamaya kosha, to stir deeper levels of union of the manifest with the unmanifest.