Ad hoc mode refers generally to a mode of operation in a number of computer systems, in which there is no central controller. It is generally used to refer to a wireless network in which there is no base station running in master mode, and simply a series of clients operating in slave mode. The phrase comes from the Latin term 'ad hoc', which equates approximately to 'improvised'.

Independent Basic Service Set (IBSS), the most basic type of IEEE 802.11 wireless LAN, is commonly referred to as an ad-hoc network. An IBSS may consists of as few as two stations. Unlike infrastructure mode, all stations are capable of communicating directly with each other.