input: There's no official creative library in DFP. You can assign existing creatives within your network to other line items. For instance, when you go into the line item, click Add creatives, and select the Use an existing creative option. This search automatically filters for the creative sizes selected for the line item. (Learn how to add an existing creative to a line item) [Term in DART for Publishers] 
output: Creative library The Creative Library centrally stores and traffics an advertiser's creatives in a DART for Publishers network. Within a network, each advertiser has a unique library into which creatives can be uploaded, stored, and assigned to ads. A trafficker can also bulk import creatives into DART through zip files.