Definition - What does Softphone mean?
A softphone is an application that enables Voice over Internet Protocol (VoIP) via computing devices, including desktops, laptops, personal digital assistants (PDA) and services like Skype and Vonage. A softphone functions like a traditional phone and is used with a headset connected to a PC's sound card.
Sometimes a softphone is designed to behave like a traditional phone and has a phone image, display panel, keypad and buttons for user interaction.
Techopedia explains Softphone
Softphone endpoints must share a communication protocol and at least one audio codec, such as Session Initiation Protocol (SIP), which is standardized by the Internet Engineering Task Force (IETF).
Skype and Google Talk apply proprietary protocols and Extensible Messaging and Presence Protocol (XMPP). Some softphones provide Asterisk’s open-source Inter-Asterisk Exchange protocol (IAX).
Softphones are used in many call centers or customer care centers, where combined phone and computer usage is required.