An entity on the Internet that is imaginary. Specifically it is a person who has created a false identity for him or herself. Generally, falsified pictures and life experience are involved. Should the person go on to actually meet those to whom he or she has been lying without taking into account that they will inevitably be caught, the condition is known as Internet ghost denial.
(Pretty girl to whom the liar is talking upon their first meeting) "Hey you aren't 6'3" or a ski instructor I bet."
"Yeah I am."
"You are a liar and an Internet ghost. In fact you are in Internet ghost denial.