In customers service field, what does the term (FACE) refer to?

Well said and good example by Vikul Bhandari.  

Face refers to each and every Moment of Truth the customer has with the company. to explain it in detail I am using an example of a telecom company. The moment of truth can be many such as the quality of network, brand promotion, response evoked after seeing an advertisement, recharge experience, call center interaction, fault repair interaction, billing in case of postpaid, etc. these all are the FACE of the company as perceived by the customer. hence it can be defined as all the experiential interactions the customer has gone through will constitute the FACE