Search engine marketing (SEM) is the umbrella discipline of driving traffic from search engines. It covers both the paid side — ads bought through platforms like Google Ads — and the organic side, SEO. In everyday industry usage, "SEM" is often shorthand for the paid channel specifically.
Paid search — search engine advertising — delivers immediate, controllable visibility for a per-click fee. Organic SEO earns unpaid rankings that build slowly but keep working without a per-visit cost. They aren't rivals; they answer different questions at different stages of a campaign. Paid is a tap you turn on for instant flow; organic is a well you dig once and draw from for years.
Suppose a B2B software company has $10,000 a month. It puts $6,000 into ads targeting bottom-of-funnel terms like "invoicing software for contractors," where a lead is worth chasing today, and $4,000 into SEO and content aimed at "how to invoice a client," building assets that will rank and convert for years. Six months in, the paid spend still costs the same per lead, while the organic pages have begun producing leads at a fraction of the cost — the compounding payoff SEM is designed to capture. Mapping that split is part of a sound SEO strategy.