It is a call which is made over internet protocol (VoIP). For example,
one can call using Google Voice to other recipient located miles away. Such
call can also be international.
Skype differs from other VoIP-systems by several factors:
Skype is very popular. During the first week in August of 2003, more than 60 thousand people downloaded the Skype-client. Today, Skype is available for the following operating systems: MS Windows, MacOS, IoS, PocketPC, Android and Linux.