WhatsApp is a messaging app that allows users to send text messages, voice messages, make voice and video calls, share images, documents, user locations, and other media. The app was founded in 2009 by Brian Acton and Jan Koum, who were both former employees of Yahoo. WhatsApp was acquired by Facebook in 2014 for $19 billion. As of 2021, WhatsApp has over 2 billion monthly active users worldwide.