A subsidiary is a company under the umbrella of your entire organization in NetSuite. If you have multiple subsidiaries you may need to set up mappings for your orders so that they post to the correct subsidiary. Typically this mapping will be a fixed value (i.e. subsidiary with internal ID 1). You can map a subsidiary on the Order and/or the Customer record if necessary. The following article explains how to set up mappings for both Orders and Customers - https://support.farapp.com/hc/en-us/articles/216791948.
To add mappings for multiple subsidiaries on orders, please see the following article: https://support.farapp.com/hc/en-us/articles/360040605474