Embargo is “the period during which the articles published in a periodical are not available in online full-text from a journal aggregator, usually the most recent one to three years. Journal publishers have established such periods to prevent libraries from canceling print subscriptions.”
Here is an example from our catalog of a journal that has an embargo period:
Psychiatry and clinical neurosciences (1323-1316)
from 02/01/1998 to 1 year ago in Academic Search Premier and Psychology & Behavioral Sciences Collection
Reitz, Joan M. Dictionary for Library and Information Science. Westport, Conn: Libraries Unlimited, 2004.