SEM (search engine marketing)

Search engine marketing originally covered every way of being found on a search engine. In current usage it nearly always means the paid side: buying ads on results pages through Google Ads or Microsoft Advertising. The unpaid side, earning organic traffic through rankings, is called SEO.

An SEM manager chooses keywords and match types, writes ads, sets bids or a bid strategy, builds landing pages and measures conversions. The goal is a profitable cost per customer.

Search arbitrage lives on the other side of the SEM manager's desk. Every click an arbitrageur monetises is a line in some SEM team's budget. When that team reviews performance by network and sees how search partner clicks convert, the result decides whether they keep paying. Understanding SEM is therefore part of understanding one's own revenue: an arbitrageur who knows how advertisers measure success can predict which traffic will keep its RPC.

Some arbitrageurs are SEM practitioners themselves. In Search-to-search they buy cheap search clicks on one engine and monetise them through a feed, which requires exactly the same skills.