Definition - What does Urdhva mean?
Urdhva is a Sanskrit term meaning "up" or "upward." This term is used in many of the Sanskrit names of yoga asanas to mean upward. Several examples include urdhva mukha svanasana (upward-facing dog pose), urdhva dhanurasana (upward-facing bow pose), urdhva hastasana (upward salute) or urdhva vrksasana (upward tree pose).
Yogapedia explains Urdhva
The opposite of urdhva is adho, meaning "downward," as in adho mukha svanasana or downward-facing dog pose. In the names of asanas, urdhva and adho are often followed by the term, mukha, meaning "face," to determine if the asanas are downward-facing or upward-facing.
Urdhva is used in the Sun Salutation sequence, which involves three urdhva poses. The sequence begins with urdhva hastasana, urdhva uttanasana (lifted forward fold) and urdhva mukha svanasana. In Ashtanga yoga, the first pose is called urdhva vrksasana, which is another name for urdhva hastasana.