iPod is a brand of portable media players designed and marketed by Apple and launched on October 23, 2001. The line-up currently consists of the hard drive-based flagship iPod classic, the high-end touchscreen iPod touch, the mid-level video-capable iPod nano, and the entry-level screenless iPod shuffle. Former products include the compact iPod mini (replaced by the iPod nano) and the high-end spin-off iPod photo (re-integrated into the main iPod classic line). iPod classic models store media on an internal hard drive, while all other models use flash memory to enable their smaller size (the discontinued mini used a Microdrive miniature hard drive). As with many other digital music players, iPods, excluding the iPod Touch, can also serve as external data storage devices.

Apple's iTunes software is used to transfer music to the devices. As a jukebox application, iTunes stores a music library on the user's computer and can play, burn, and rip music from a CD. It also transfers photos, videos, games, and calendars to those iPod models that support them. Apple focused its development on the iPod's unique user interface and its ease of use, rather than on technical capability. As of October 2007, the iPod had sold over 119 million units worldwide (stated in "The Beat Goes On" conference) making it the best-selling digital audio player series in history.

iPod can play MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless audio file formats. The iPod photo introduced the ability to display JPEG, BMP, GIF, TIFF, and PNG image file formats. Fifth and sixth generation iPod classics, as well as third generation iPod nanos, can additionally play MPEG-4 (H.264/MPEG-4 AVC) and QuickTime video formats, with restrictions on video dimensions, encoding techniques and data-rates. Originally, iPod software only worked with Macs; however, starting with the second generation model, iPod software worked with Windows and Macs. Unlike most other media players, Apple does not support Microsoft's WMA audio format — but a converter for WMA files without Digital Rights Management (DRM) is provided with the Windows version of iTunes. MIDI files also cannot be played, but can be converted to audio files using the "Advanced" menu in iTunes. Alternative open-source audio formats such as Ogg Vorbis and FLAC are not supported without installing custom firmware onto the iPod.

The iPod is associated with one host computer. Each time an iPod connects to its host computer, iTunes can synchronize entire music libraries or music playlists either automatically or manually. Song ratings can be set on the iPod and synchronized later to the iTunes library, and vice versa. A user can access, play, and add music on a second computer if the iPod is set to manual and not automatic sync, but anything added or edited will be reversed upon connecting and syncing with the main computer and its library. If a user wishes to automatically sync music with a another computer, the iPod's library will be entirely wiped and replaced with the other computer's library.

iPods with color displays use anti-aliased graphics and text, with sliding animations. Classic iPods have five buttons and the later generations have the buttons integrated into the click wheel — an innovation which gives an uncluttered, minimalist interface. The buttons perform basic functions such as play, next track, etc. Other operations such as scrolling through menu items and controlling the volume are performed by using the click wheel in a rotational manner. iPod shuffle does not have a click wheel and instead has five buttons positioned differently from the larger models. iPod touch uses no buttons for any of these functions, instead relying on a Multi-touch input style similar to that of the iPhone.


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