Google Analytics identifies each visitor to a website with a unique ID, and the first time someone reaches a site from a new device or browser, that visit counts as a New User. Every new ID Google Analytics registers counts toward this metric. Since the ID lives in the browser, and by extension the device, the same person visiting from a different device or browser shows up as another new user with another new ID. Visit again from that same browser, though, and Google Analytics counts it as a returning user instead.
The metric is a rougher proxy for real audience growth than it looks. Clearing cookies, switching browsers, or using a phone and a laptop for the same task all generate fresh IDs for the same actual human, which means New Users tends to overcount unique people rather than undercount them. It's most useful as a directional signal, is a campaign or content push actually reaching people who haven't been on the site before, rather than as a precise headcount of individuals. Reading it alongside returning-user counts gives a fuller picture: healthy growth usually means both numbers moving in a reasonable balance, not just new users climbing while nobody ever comes back.
