"Manila" is a type of which of these common office staples?

A manila envelope is a tan-colored vessel that is designed for storing or transferring important documents. Manila is a type of paper that is thicker and more durable than standard materials and can come with a protective lining that will keep contents dry and free of contaminants. These envelopes are also sized to ensure that the papers being held inside can fit without the risk of being folded or wrinkled.

Source: Staples