peripheral
noun
electronic equipment external to the circuit board that contains the CPU of a computer
“disk drives and printers are important peripherals”
adjective
on or near an edge or constituting an outer boundary; the outer area
“Russia's peripheral provinces”
“peripheral suburbs”
Oppositescentralrelated to the key issue but not of central importance
“a peripheral interest”
“energy is far from a peripheral issue in the economy”
Source: WordNet 3.1, Princeton University