Double sinawali is a technique in arnis, escrima, and kali that involves striking with both arms in parallel opposing motions, mimicking the crisscross pattern of woven bamboo mats. It consists of 6 strikes - 3 strikes alternating between the right and left hands, with each strike comprising a high forehand, low backhand, and high backhand strike. Learning double sinawali is important for arnis because it builds skills in double motion striking with both arms simultaneously.