Fappying is continues form of the word Fap. Fappying is an act of masturbation that is happening now or over a period of time in the present. It is formed by combining the appropriate form of the auxiliary verb "to be" (am, is, are) with the present participle of the main verb.
Fappying (to be form of FAP or Masturbation) is the act of self-stimulation of the genitals to achieve sexual pleasure in present continuous tense.
Please note that the usage of "Fappying" or "FAP" is considered to be vulgar slang, and it is generally not appropriate to use it in formal or professional settings.