Bid term explained
Bid is the maximum price you are willing to pay the advertiser for a click on their advertising (or Cost Per Millenium) bid is called. Bids come from Internet auctions, where each participant offers a price in order to obtain the desired result. In advertising this result allows the advertiser to be above the rest and thus have a great CTR on your ad.
Bids is also used in freelance when freelancers offer the price at which they are willing to do the work (to design, develop, script, etc.).
Bid means the price offered. In SEO the term Bid is most often used with the purchase of contextual advertising in such services as AdWords or Yandex.Direct, and when the earnings on their sites with AdSense.