The main difference between SEO and SEM is this: SEO is free and a search-based organizational strategy, while SEM comes in price and sells-based. SEO spends time to take effect when SEM is instant.
Search Engine Optimization is used for website owners to rank higher in SERPs and attract more traffic to their websites. Their ranking is to ensure the website performs well, known characteristics and basic content, and includes keywords that are relevant to the user's query. A website deserves a place in SERPs, performance is natural, organic, and so it's free.
Search Engine Marketing is used by website owners to take advantage of a high level of paid advertising through SERPs.
Other differences between SEO and SEM:
• Increase the SEM search for the user to appear on the map, while the results of the SEO efforts do not.
• SEM issues feature to extensions, SEO event messengers have.
• The website owner pays every time someone clicks on the ad. Website owners pay nothing when a user clicks on their page.
• SEO efforts add value to the page over time. SEM efforts are immediate and provide no lasting value.