What's 'metaverse', concept around which Facebook is said to be changing name?

Facebook reportedly plans to change its name to reflect its focus on building 'metaverse', the concept that generally refers to shared virtual world environments which people can access via the internet. 'Metaverse' can refer to digital spaces made more lifelike by the use of virtual reality or augmented reality. Some people also use the word 'metaverse' to describe gaming worlds.