SEM is called "Search Engine Marketing'' in English which includes search engine advertising and SEO. 

What is SEM? 

Search Engine Marketing (SEM) meaning describes the paid advertising appearing on a search engine results page.

Which is better between SEO and SEM?

The main difference is that Search Engine Optimization (SEO) focuses on optimizing a website in order to get traffic from organic search results. The goal of Search Engine Marketing (SEM) is to get traffic and visibility from both organic and paid searches.

For SEO, the effect is relatively slow, but the click ranking and optimization time is shorter now. One way is to spend money on original website content and old domain names, and the other way is to spend money to simulate clicks from real users. 

How to choose between SEO and SEM?

If you have a budget to spend, then you may consider both options. However, if budget is a consideration, then SEO is a better choice. SEO is still reliable if there is a trusted team. Otherwise, paid SEM may be more appropriate.

For some website projects that need to quickly grab the market opportunities, try to choose SEM. 

SEO is better for some long-term projects. By publishing articles to optimize keywords, you can increase traffic, gain user trust, eliminate negative news on the Internet, increase user clicks, and effectively increase brand awareness. However, the disadvantages of SEO are slow effect, high optimization risk, high team communication cost, and unstable traffic.

It's worth noting that SEM is search engine marketing, where SEO is only part of SEM.