Normally when freight arrives in the US, a Customs entry is filed at the port of arrival. If it comes into Los Angeles, it is Customs cleared in Los Angeles (all import freight must be approved by US Customs before it can be released into the commerce of the US).
Sometimes however, it is beneficial for importers to move freight to another Customs port and to file a Customs entry there. In that case, Customs assigns an IT number to grant permission to the importing carrier to move the freight prior to clearance to another Customs approved, bonded warehouse in another port. IT numbers or (Inbond Transit) numbers come in several formats – they can be nine numerical digits, they can start with a V for ocean shipments, or they can be the same number used on an air shipment master bill.
The IT number must be properly reported to US Customs when the import broker files the entry. Freight said to be “moving on an IT” is traveling inbond from the port of entry to another port for clearance.