Hard to pick. "'Metaverse" itself is really just an umbrella term, referring to a convergence of various technologies and concepts. Except for the obvious choices (VR, AR, avatar, land, etc.), I'd go with the following three: datafication, decentralization, and FUD.
Datafication refers to the collection of data on an individual's surroundings and behaviors while in virtual reality, with headsets able to track and gather information on hand movements, objects in the (physical) environment, and more. Twenty minutes in VR collect two million pieces of data!
Decentralization refers to distributing power and property on the web, allowing for a more democratic and disintermediated decision-making process when compared to Web2.
FUD is an acronym that stands for "fear, uncertainty, and doubt." It is a tactic used in PR, business, and propaganda to manipulate public perception about a particular product, technology, or individual by spreading misinformation that generates negative emotions and creates uncertainty or doubt about a subject. In the metaverse space, FUD is often used to describe general skepticism or negative attitudes toward virtual, augmented, and extended worlds, but it can also be employed by supporters of a specific company to deflect criticism.