A computer mouse is a device used for pointing to objects on a computer monitor, and selecting them. It can be moved around on a flat surface. Those movements are transmitted back to the computer and move a pointer on the screen in the same direction. The mouse usually has one or more buttons that can be pressed to select items on the screen and execute commands. On most modern mice, one finds at least a primary and secondary button, and often third or fourth buttons. The primary button is designed to be used with the index finger, while other buttons are often positioned to be used with the other fingers. Many mice also contain a scroll wheel, which can be used to scroll in documents.
Up until a few years ago, mice tended to be made by having a rubber ball that would roll around and move sensors inside the mouse. These had one major disadvantage: the ball picked up dirt, which could clog the sensors, and which required periodic cleaning. Today, these have mostly been replaced with optical sensors, which emit a coloured light (usually red) and measure the reflections from the mousing surface to determine movement. Mice today are now available that use wireless transmission -usually radio, sometimes Bluetooth, and occasionally infra-red, and wired mice are now extremely cheap to purchase.
Despite their prevalence, not all tasks can be best accomplished using the mouse - there are still a number of applications optimized for keyboard input (especially command line applications), and many of these tend to be preferred by programmers, power users and those who have learned how to touch type. For other tasks, especially involving the manipulation of graphics, the mouse is unavoidable. On laptop computers, trackpads are often provided in place of the mouse, although some laptops provided a small rubber 'trackpoint' (sometimes referred to as a 'nipple'). Trackballs are occasionally used in place of mice.