What is "leidang"

The institution known as leiðangr ( Old Norse), leidang ( Norwegian), leding ( Danish), ledung ( Swedish), expeditio ( Latin) or sometimes lething ( English), was a form of conscription to organise coastal fleets for seasonal excursions and in defence of the realm typical for medieval Scandinavians and, later, a public levy of free farmers. In Anglo-Saxon England, a different system was used to achieve similar ends, and was known as the fyrd.