What is the difference between SEO and SEM?

SEO (Search Engine Optimization) = the work you do to rank organically in unpaid search results. SEM (Search Engine Marketing) = paid Google Ads that show above organic results. SEO compounds over time at lower ongoing cost. SEM works immediately but costs every click. Most successful small businesses do both: SEM for quick wins on high-intent keywords, SEO for the long-term traffic moat.