Keywords: words or (groups of words) entered into search engines in order to get matching and relevant results.

Brainstorm and make a list of keywords to focus on when you begin adding content to your website. Try and imagine what users would type into Google, to find your type of product or service. Each "keyword" can be 1-4 words long.
These keywords are what you want search engines, like Google, to recognize as being important in connection to your website. For example, if you are a car dealership, just having the keyword 'jaguar' would be lost as there are so many alternatives. Instead, consider using 'jaguar cars', 'jaguar parts', etc.

Check out the Wix Blog post on the topic here.