Starting May 21, 2018, Google will transition from Hangouts video meetings to Hangouts Meet. Meet provides significantly better performance over classic Hangouts video calls, with a cleaner, more focused user experience and a simple, secure, and reliable method for guests to join meetings. With Meet, participants can now use a standard telephone call to join a session.
With this transition, newly created Calendar events will contain Meet video meeting details. Previously created classic Hangouts video links will still be usable until August 13, 2018. For a full comparison of existing and coming features between classic Hangouts and Meet refer to this Help Center article.
Please note: There are many services under the Hangouts name, including Hangouts chat, Hangouts meet, and Google Hangouts. Hangouts Meet is the video meeting service that has become the standard in the Google portfolio.