The tracking system used by USPS will sometimes indicate the following:

The U.S. Postal Service was electronically notified by the shipper or shipping partner on XXX XX, 200X to expect your package for mailing. This does not indicate receipt by the USPS or the actual mailing date. Delivery status information will be provided if / when available. Information, if available, is updated every evening. Please check again later.

If the tracking number gives this message your item has been shipped, and may even be delivered, but the USPS system will not update for several days. This is normal for USPS. If it has been > 10 business days without arrival, please stop by or call your local post office to see if they're holding the package for you. A phone call to the local post office can get more information than is available online at www.usps.com.