certificate of sponsorship (cos) reference number
If you hold a Tier 2 or Tier 5 sponsor licence, you are permitted to hire non-EEA nationals under either a restricted or unrestricted Certificate of Sponsorship (CoS). A CoS is a unique reference number allowing the sponsored employee to make their visa application. All Tier 2 unrestricted Certificate of Sponsorship allocations are subject to a fixed allocation period that runs from 6th April to 5th April the following year. The number of restricted certificates available is capped each year.