Search Engine Marketing, or SEM, refers to paid efforts to gain visibility on search engines, while SEO focuses on organic results. The most common paid model is PPC, or Pay-Per-Click, in which advertisers pay only when a user clicks their ad. Google Ads is Google's flagship advertising platform, supporting search ads (text ads that appear on the SERP for specific keyword queries), display ads (visual banner or image ads shown on websites, apps, and videos in a display network), video ads, and more. A specialized format, Google Shopping, displays product images, prices, and merchant names as product listing ads, driven by a product feed, a structured file listing product data such as titles, prices, and images.
Search and shopping campaigns revolve around keywords and match types, settings that control how closely a user's query must match the advertiser's keyword to trigger an ad. Common match types include broad match, phrase match, exact match, and negative match, with negative keywords used to exclude irrelevant searches. Two core pricing metrics structure this ecosystem: CPC, or Cost Per Click, is the amount paid per click, and CPM, or Cost Per Mille, is the cost per one thousand ad impressions. Ad performance is tracked through CTR, the Click-Through Rate, calculated as Clicks divided by Impressions multiplied by 100, and ROAS, or Return On Ad Spend, calculated as Revenue from Ads divided by Cost of Ads. Marketers also think about break-even ROAS, the level at which ad revenue exactly covers ad costs, derived from margin and pricing.
How ads are positioned and how much they cost is determined by Ad Rank, a value based on the advertiser's bid, the Quality Score (a rating of keyword and ad relevance and landing page experience), and other factors. Bidding strategies can be manual or automated; common automated approaches include Maximize Conversions, Target CPA, and Target ROAS, all of which let the ad platform's algorithm set bids to meet specific campaign goals. A landing page in SEM is the specific page users reach after clicking an ad, and best practice calls for strong message match, meaning consistency between the ad's promise and the page's content, along with a clear headline that communicates the main benefit.
Paid social advertising extends these principles onto social platforms. Advertisers can build custom audiences from website visitors, email lists, or app activity, and create lookalike audiences to find new people similar to an existing source audience. Over time, campaigns may suffer from creative fatigue as audiences see the same ads too often and stop responding, which is why ad frequency capping (limiting how many times an individual user sees an ad) and ongoing creative testing are important. Dynamic remarketing, which automatically shows ads featuring specific products a user previously viewed, is a powerful ecommerce tactic that often pairs with a remarketing window, the number of days after an interaction during which a user remains eligible to see retargeting ads.