What is the difference between SEO and SEM?

The answer

SEO aims to earn unpaid visibility in search results, while SEM, or Search Engine Marketing, is a broader term that often includes paid search advertising as well as SEO. With paid ads you set a budget and the visibility generally stops when the spending stops. SEO builds up more gradually and does not stop when you pause a campaign. Many businesses use both, and neither replaces the other. Ads do not influence organic rankings.