I'm reading the Tibetan Book of the Dead.[1] On page 46 there's a compact yet accurate definition for the term 'yoga'. They are quoting Walter Evan-Wentz. He wrote in English but this book translated his words into Dutch. I will translate them back into English:

Yoga derives from a Sanskrit word that means yoking, connecting. A concatenating of the biological nature to the divine nature inside the human, such that the higher one controls the lower one.

Yoga is the scientific method of making the mind lucid and transparent, so that the light of Reality can be reflected and the person can know himself.

In the same way that gold can be purified by chemical means, Truth can be separated from delusion through yoga.

It's slightly coloured by adherency but still well balanced with precision. I no longer care too much about all information being exclusively academic. There are plenty of times when adherents of some doctrine provide useful information and this is especially true for Eastern wisdom since the contents by themselves are profound.

The use of this definition is to communicate the distinction between yoga and physical exercise in an accessible way. I find that even books that promote exercise will often still include a good description of the authentic yoga, although those initial pages are the only thing those books are useful for.

1. The Tibetan Book of the Dead, translated by Kazi Dawa-Samdup, edited by W. Y. Evans-Wentz, Oxford University Press, 1927.