taru-adjective, adverb taking the 'to' particle
in good order; orderly; well-organized
Describes a state where things are arranged neatly and systematically, often used in formal or written contexts. Functions as a taru-adjective or adverb with と.
The documents are arranged in perfect order.
His desk is always well-organized.
整然 alone means 'orderly' or 'systematic' and is more common. 秩序整然 adds the nuance of overall order or system, emphasizing a broader state of organization.
A four-character compound combining 秩序 (order, system) and 整然 (orderly, systematic). The exact historical derivation is uncertain, but it follows a common pattern of reinforcing meaning through synonymous components.