1 [data quality] A measured, observed, calculated, or interpreted value that differs from the true value or the value that would be obtained by a perfect observer using perfect equipment and perfect methods under perfect conditions.
2 [data quality] In a GIS database, a spatial or attribute value that differs from the true value. Error may also be understood as the totality of wrong or unreliable information in a database. Spatial errors are mainly errors in position (feature coordinates are wrong) and topology (features do not properly connect, intersect, or adjoin). Attribute errors are wrong quantities or descriptions associated with features, or missing or invalid values. Errors enter a GIS database through various processes, including data collection (for instance, flawed instruments); data conversion (for example, map digitizing mistakes); data entry and editing; data integration (for example, mixing data at different scales); spatial data processing (for example, inaccuracies caused by generalization); and data analysis (for example, features assigned to inappropriate categories on the basis of flawed criteria).
3 [ESRI software] In geodatabase topology, violation of a topology rule detected during the validation process.
4 [programming] In computer programming, a piece of code that prevents a program from compiling or running; also, program logic that makes a program end prematurely, go into an endless loop, or give incorrect results.