VSOE - Definition from ASU 2009-14, Topic 985-605

A vendor must sell or intend to sell a particular element separately to assert vendor-specific objective evidence for that element.  If a vendor does not have VSOE for the undelivered elements in an arrangement, the revenue associated with both the delivered and undelivered elements is combined into one unit of accounting.  Any revenue attributable to the delivered products is then deferred and recognized at a later date, which in many cases is as the undelivered elements are delivered by the vendor.