SEA which stands for Search Engine Advertising, it consists of activities of creating and optimizing search ads for high performance. The aim of search ads is usually conversions and the activities performed are usually towards this target. This is because you can easily target audiences and terms with laser focus on specific user actions (phone calls, clicks, purchases, etc..).
SEA can be short and long-term game, it is highly affected by the competition. Competitors with high paid budgets can force smaller players out of this channel. SEA, as with any ad platform stops bringing in traffic as soon as you stop paying for it. On the other hand, you can get traffic immediately without the need to invest for ranking upfront as we have to with SEO.