Operability is an engineering term concerning the qualities of a system which make it work well over its lifetime, and software operability applies these core engineering principles to software systems.
An operable software system is one which delivers not only reliable end-user functionality, but also works well from the perspective of the operations team. Such software has been built to operate successfully without needing application restarts, server reboots, load-balancer hacks, or any of the countless other fixes and work-arounds which operations teams have to use in order to make many business software systems work in practice on a daily basis.
Software systems which follow software operability good practice will tend to be simpler to operate and maintain, with a reduced cost of ownership, and almost certainly fewer operational problems.
Product delivery teams with a DevOps approach will generally produce systems with better operability than teams split into the traditional Dev + Ops silos. Most organisations today are still in this siloed world of Dev + Ops, but by gaining a better understanding of software operability, many engineering teams will move instinctively towards a DevOps model.