SERP stands for Search Engine Results Page. Search engines are Google, Yandex, Baidu, Bing, and Yahoo. They build their results page based on country, language and locale, mobile or desktop. Keyword position is an exact place of your website's position for a particular search term in a search engines' result pages. The lower the position, the easier your website is to find in search results for that specific keyword.
It is absolutely necessary for any websites to monitor their keyword ranking. One of the most common mistakes website owners make is that they have content (pages, posts, articles) without targeting any keywords at all. Whether your keywords have already been getting high positions in search results or has just begun reaching early positions in the SERP, you should always know where they are on the top 100 list.