The reason the link was discovered during the last crawl: the page was crawled for the first time, the link was added to the page, or the link re-appeared after being removed
An estimation of the average monthly number of searches for the top keyword over the latest month or over the latest known 12 months of data depending on the "volume_mode" parameter
An estimation of the average monthly number of searches for the top keyword over the latest month or over the latest known 12 months of data depending on the "volume_mode" parameter