Definition - What does Ardha mean?
Ardha is a Sanskrit word which means "half." The word is used in the names of certain yoga poses which are an intermediate version of their complete counterparts, as in ardha matsyendrasana, an intermediate asana of matsyendrasana. Poses that include "ardha" in the name can be practiced by beginner yogis, then advance to the complete expression of such postures.
Yogapedia explains Ardha
Ardha padmasana (half lotus pose) is the intermediate pose of padmasana, which is the recommended seated posture for meditation. This posture opens the hips, promotes calm and improves focus.
Ardha matsyendrasana is also known as half lord of the fishes pose as well as half spinal twist pose. This posture twists, tones and energizes the spine, relieves fatigue and promotes flexibility. Ardha chakrasana is an intermediate variation of chakrasana, or wheel pose. The posture tones the back, relieves back pain, stimulates the abdominal organs and reduces excess fat in the waist.
Other poses with "ardha" in their names include: ardha dhanurasana, ardha baddha padmottanasana, ardha chandrasana and ardha ustrasana.