Shared software is a different term used to describe free software

Free software

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 and open source software, and possibly also software that is not formally covered by the definition of either, but that is in some other way shared rather than owned. The term has been used to transcend the awkward debate over what to call this type of software.

It may also pertain to software that is not free software

Free software

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 or open source software, but shared between business units within a corporation.