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]