A mobile operating system is an operating system used for smartphones, tablets, smartwatches, smartglasses, or other non-laptop personal mobile computing devices. While computers such as laptops are "mobile", the operating systems used on them are usually not considered mobile, as they were originally designed for desktop computers that historically did not have or need specific mobile features. This "fine line" distinguishing mobile and other forms has become blurred in recent years, due to the fact that newer devices have become smaller and more mobile, unlike the hardware of the past. Key notabilities blurring this line are the introduction of tablet computers, light laptops, and the hybridization of the 2-in-1 PCs.
Mobile operating systems combine features of a desktop computer operating system with other features useful for mobile or handheld use, and usually including a wireless inbuilt modem and SIM tray for telephone and data connection. In 2024, approximately 1.22 billion smartphones were sold globally, marking a 7% increase over the previous year and a solid rebound after two consecutive years of declines. Sales in 2012 were 1.56 billion; sales in 2023 were 1.43 billion with 53.32% being Android. Android alone has more sales than the popular desktop operating system Microsoft Windows, and smartphone use (even without tablets) outnumbers desktop use.