Typically if a keyword has low impressions it means, for the parameters you're targeting, there aren't enough people searching for your keyword. Impressions occur any time someone has typed some broad iteration of your keyword (for broad match). If it doesn't have impressions, it means people aren't using that keyword. Could be seasonal shifts in the market or it simply may not be a popular search phrase people use in the location you're targeting. If I were you, I'd try looking through keyword planner for higher volume keywords. I would start troubleshooting and optimizing if I had a relevant keyword that was getting high impressions and no clicks.