A keyword is a word or phrase people type into search engines (like Google) to find information. For example, if you run a cake shop and want more customers to find your website, a good keyword might be “best chocolate cake recipe.” Another example could be “cheap wedding cakes.” These are phrases that actual customers might type into Google when searching for a cake shop. And even though these phrases consist of more than one word, they are still keywords.
When someone types a keyword into Google, Google looks for webpages that match what the user is looking for and shows those pages in the search results. If your website has those words and provides helpful information, Google is more likely to show your page in those search results. This is why keywords are important: They help Google understand what your page is about and who should see it.
Further reading: What Are Keywords & How to Use Them