In [[resistivity]] well logging, an electrical terminal in that part of the electrical circuit exposed to the drilling [[mud]] or drilled [[formation]] wall. The electrode is the electrical contact between the electrical circuit of the measuring device and the medium which is to be measured. The electrode can be a current electrode, through which electrical current enters or leaves a medium; or it can be a measure electrode, which is used for measuring the [[potential]] resulting from the flow of electric current. Also used in [[SP]] logging. See [[A electrode]] and [[M electrode]], also [[normal device]] and [[lateral device]].