Surprized you ask that, after all you've used the abbreviation in your second last post yourself...
Anyway, VEX is the abbreviation for Virgin Express, a Brussels-based low cost operator (partly) owned by Sir RB. Before Sir RB became the owner, VEX was called EBA-EuroBelgian Airlines, which was created from the remains of bankrupt TEA. VEX used to be a pure charter operator, but after strong competition from Sabena's charter subsidiary Sobelair, VEX had to stop the charters and turned themself into a no frills, low fare airline.
VEX managed to secure a deal with Sabena in which they became a kind of subcontractor on one dense shorthaul route (LHR) and on several touristic destinations like Barcelona, Faro and Rome.
Over the years VEX became more end more dependant on these Sabena flights; last year for instance those Sabena flights ment more then 40% of the production at VEX, but with the end of Sabena came also an end to the subcontract.
VEX now tries to fly several routes on their own, but with very limited financial success (as they admit in a recent press release), so a linkup with New Sabena would -from a shareholders point of view- be a logic thing to do.