A daily count of keywords that physically can't compete - their bid is below the first-page bid, or they're rarely served. Rather than one alert per keyword (which could be hundreds), it gives you a single grouped finding per campaign, and only once enough keywords are affected to matter.
Defaults & settings
Below first page bid - count keywords whose bid is too low to show on the first page. On by default.
Rarely served - count keywords that almost never trigger an ad. On by default.
Low quality score - also count keywords marked low quality. Off by default (noisier).
Minimum keyword count - only flag a campaign when at least this many keywords are affected; one rolled-up finding per campaign. Default 10, adjustable 1-100.
Checks daily; 72-hour cooldown.
Example. After a CPC-inflation month, 23 keywords in one campaign slip below first-page bid. You get one dashboard entry saying so - a bid-strategy review, not 23 pings.