A Google Surge, also known as a Google Blast or just a network blast, is a form of ad buying that uses Google AdWords to create a large amount of short-term advertising. If a surge is large enough, it could reach virtually every person who surfs the Web in a geographical area, because nearly everyone hits a website with Google advertising on it during the day. This isn't a formal Google product, in other words, but a way of using Google's ad tools for targeted campaign marketing.
Think of this as the Google equivalent of buying all the ad time slots from the local networks, or perhaps it's the Google equivalent of putting a campaign sign in every yard in the city.
Who Uses Google Surges?
Google Surges are most useful in politics. They're expensive and short-term, so there are very few other areas where you'd want to drop a huge amount of money on a massive advertising campaign to get everyone to see your message. In nearly all other cases, you'd want to selectively target ad campaigns, so you weren't wasting your ad words on the wrong audience. The last days before an election are a fine time to blast out a campaign message.
The term Google Surge likely came from Eric Frenchman, who used the technique as part of his online marketing strategy in several Republican election campaigns. Most recently, the liberal blog Daily Kos launched a week-long Google Surge campaign against a Wisconsin Republican to call attention to a political controversy.