'unlogged' originates from English, specifically formed from the negative prefix 'un-' (from Old English 'un-' meaning 'not') combined with 'logged' (the past participle of the verb 'to log', derived from the noun 'log'—a written record).

'logged' developed from the noun 'log' (a record, from nautical practice of keeping a 'logbook'); the verb 'to log' (to record) produced the past participle 'logged', and the adjective 'unlogged' was formed by adding the prefix 'un-' to mean 'not logged'.

Initially it meant simply 'not marked in a log/record'; over time it retained that technical sense (especially in computing) and also came to be used in contexts referring to timber/forestry to mean 'not felled'.