Data Freshness is how long Google Analytics takes to collect and process a hit from your website, app, or device, and then makes the data available via the Analytics interface or API. If that process takes 20 minutes, then Data Freshness = 20 minutes.
As our Google Analytics integration pulls data via the Google Analytics API, this means the numbers on your dashboard are subject to some restrictions Google puts in place that can sometimes result in different, under-reported data being shown.
If you see a Google Analytics widget showing '0' or a much lower number than expected, one possible reason for this is that the data endpoint Geckoboard hooks in to has a delay applied to it. On some larger Google Analytics accounts that require a large amount of user data to be processed on any given day, your data may be delayed by up to 48 hours. Read more about Data collection limits.