I believe that you are referring to the "Hub Summary". You can create your own Hub Summary (recommended) or Google will create one for you. I have found that Google's auto-generated descriptions can be awkward and not on target with your Hub content.
If you go to "My Account" where you can edit your Hubs, you may notice an "A" right after your individual Hub links. This means that you are missing a custom summary. If you click "Edit" on your Hubs, (one at a time) and you look at the tool bar to the right, you will see a few fields (reorder, tags, settings, Summary, groups).
Click on "Summary" and you can enter 2-5 sentences that describe what your Hub is about. This allows people to get a "preview" of what your page is about when they find it in search engines. For more information on how and why to add summaries to your Hubs, follow this link to the HubPages Learning Center: https://hubpages.com/community/Learning-Center-How...
Hope this Helps!