Not really a Norwegian word; 'flate pakker' would be flat packages, while 'flatpakker' could be the present tense of a contrived verb 'å flatpakke' - to package <things> in a flat shape. "Fabrikken flatpakker møblene for forsendelse" - the factory packages the furniture flat for shipment.

there are many types of flat packs, e.g. furniture from IKEA comes flat packed, batteries can come in flat packs. If you search on google you will find loads of hits but without further info. I cannot provide a specific context.