Mini-ATX

Mini-ATX, or Mini ATX, is the name of any of several motherboard form factors that are slightly smaller than Mini-ITX. Though there is no official standard, Mini-ATX (advanced technology extended) dimensions are usually 5.9" x 5.9" (105 x 105 mm). They are intended for use in smaller computers that are power efficient and generate little heat, such as HTPCs.

FlexATX, Form factor, Micro ATX, Motherboard terms, Standard ATX