Several fingers pluck several strings with a closing motion. The strings are not adjacent to each other and are less than an octave apart. Sources disagree on the specifics.
Lee says He Xian is for two strings plucked while Jian Xian is three played as a chord.
Kwok says He Xian is for three or more strings while Jian Xian is for two.
Ferguson’s various sources agree two strings are plucked although the number of strings between the two strings can vary. His sources disagree as to which two fingers are used to pluck the two strings.