If a keyword's search volume shows "pending" within the platform, that means 1 of 2 things:

1) The keyword was recently added and we are in the process of retrieving search volume for the keyword. This will take about 24-48 hours. 

2) The exact keyword is not returned as a result in Google's Keyword Planner and thus the search volume isn't retrievable. Typically, Google's Keyword Planner does not return results for keywords with non-standard characters such as ! @ % , *. 

For more information on keywords with low search volume:: https://support.google.com/adwords/answer/2616014?hl=en.

If the keyword has a Search Volume of 0 within the platform, then Google does not report any Search Volume for this keyword.

Learn More about Keyword Planner's search volume updates