Google is attempting to delete any of the Google+ page listings that have not been recently utilised. Each of these pages are a social media profile for your business and up until recently there were posts added to most of these accounts like you would for Facebook or Instagram.
In the past when a business map was setup it would automatically create a Google + page for the business too. You could also create a stand alone business page (without a map). Note that your map and page listing are separate though so Google deleting the + page shouldn't impact your reviews or map content.
You can search for your current business page here - https://plus.google.com/
Google has not yet disclosed whether they are deleting Google+ all together but they are certainly cleaning up listings that are orphaned. So if you start utilising these business pages as part of your social media management in the next week or so then they will not be deleted and you continue to run.
If you are not sure whether to continue running your Google+ page please contact us to discuss this in further detail.