Classical Ashtanga Yoga refers to the 8-limb path toward Self-realisation as outlined in Patanjali's "Raja Yoga Sutras":

1. yamas  -  ethical rules concerning society
2. niyamas  -  ethical observances concerning oneself
3. asanas  -  postures
4. pranayama  -  control of energy
5. pratyhara  -  withdrawal of the senses
6. dharana  -  concentration (focus with effort)
7. dhyana  -  meditation (focus without effort)
8. samadhi  -  bliss

Not to be confused with "Ashtanga vinyasa" or "Ashtanga yoga" which in recent times refers to a very specific hatha yoga lineage.