Fingering is a sex act involving a person sexually stimulating the vulva (externally) and/or vagina (internally) of another person by using the fingers. It may also include the use of the fingers to stimulate the anus, anal canal, and/or rectum.
Mind that Fingering can also be done by oneself, which would qualify as Auto-Fingering or Self-Fingering. Fingering can be considered the “female version” of the male Handjob.
In any case, the main goal of Fingering is to increase sexual pleasure and sexual arousal of the receiver, which could be a means of foreplay or a direct means to achieve an orgasm and/or female ejaculation.
In male-female interaction it may be an alternative to penile-vaginal intercourse in order to avoid sexually transmitted infections (of course, the hands need to be kept clean before and afterwards), to avoid pregnancy, or to preserve virginity.
Fingering is typically carried out by stroking, circling, tugging, and/or rubbing the vulva (and clitoris) with the hand and fingers, and internally manipulating or massaging the vagina and its various erogenous spots.
Notably when Anal Fingering (Rectal Fingering) is included in the act it’s advised to use a lubricant to increase the pleasurable sensation and to support entering the anal canal rectum.