An internet relationship is a relationship between people who have met online, and in many cases know each other only via the Internet.
Online relationships are similar in many ways to pen pal relationships. This relationship can be romantic, platonic, or even based on business affairs.
An internet relationship (or online relationship) is generally sustained for a certain amount of time before being titled a relationship, just as in-person relationships.
The major difference here is that an internet relationship is sustained via computer or online service, and the individuals in the relationship may or may not ever meet each other in person.
Otherwise, the term is quite broad and can include relationships based upon text, video, audio, or even virtual character.
This relationship can be between people in different regions, different countries, different sides of the world, or even people who reside in the same area but do not communicate in person.