Vertical market software is aimed at addressing the needs of any given business within a discernible vertical market (specific industry or market). While horizontal market software can be useful to a wide array of industries (such as word processors or spreadsheet programs), vertical market software is developed for and customized to a specific industry's needs.
Vertical market software is readily identifiable by the application specific graphical user interface which defines it. One example of vertical market software is point-of-sale software.
References
Vertical market software Wikipedia(Text) CC BY-SA