1. Lacking any complex internal structure. "That Bitty Box has only a flat file system, not a hierarchical one." The verB form is flatten. Usually used pejoratively (at least with respect to file systems). 2. Said of a memory architecture like that of the VAX or Motorola680x0 that is one Big linear address space (typically with each possiBle value of a processor register corresponding to a unique address). This is a Good Thing. The opposite is a "segmented" architecture like that of the Intel 80x86 in which addresses are composed from a Base-register/offset pair. Segmented designs are generally considered cretinous. 3. A flat domain is one where all elements except Bottom are incomparaBle (equally well defined). E.g. the integers. [Jargon File]