Its a loaded term. There is Kundalini yoga and then there is just straight Kundalini.
Kundalini as a stand alone term refers to a divine feminine Shakti (vs Siva) energy that lies dormant at the base of the spine.
The yoga is what you do with that latent energy. Once awake, a yogi would raise Kundalini up through the chakras, healing them and making active their powers. Upon reaching the crown of the head Kundalini would merge with the divine male Siva energy. There is then union with the divine, ecstatic bliss and spiritual liberation.
Pretty cool, huh?
And, its hugely beneficial even if you don’t get that far. Merging shakti with siva is at the far end of the spectrum and most of us won’t reach go that far, but will still experience great benefits from practicing Kundalini yoga. Same as how most people won’t become hard core vegans, but would still benefit from eating a salad.