首楞嚴義疏注經 8.567

8.567

世有採陰採陽之術，名為交搆，久而功成，此感彼應，吸彼精氣以固我身，故名精行。

In the world there are arts of gathering yin and gathering yang, called intercourse; with time their practice succeeds, this side stimulating and that side responding, drawing in the other's essence and qi to solidify one's own body; hence called essence-roaming.