Facebook's instant messaging service, which is available on the Facebook website and as an app for mobile devices. Introduced in 2011, and initially bundled into the Facebook mobile apps, instant messaging was separated into the stand-alone Messenger app in 2014. As of 2015, Facebook Messenger (700 million users) and Facebook's WhatsApp instant messaging (800 million) exist as separate services. In 2015, a virtual assistant was added to Messenger (see Facebook M). See WhatsApp Messenger and Facebook.