A keyword is the word or phrase a customer types into Google when they are looking for something, like plumber near me or gentle dentist for kids. It is the exact language of the search, and the phrase your pages need to match to show up for it.
For a small business, keywords are the bridge between what you offer and how people actually ask for it. The words you use for your own work are often not the words a customer uses. You might call it residential HVAC maintenance while they type why is my house so cold upstairs. A page that speaks their language, plainly and specifically, is a page their search can find; one written only in industry terms quietly misses them.
The practical move is to write each page around one clear thing a real person searches for, in their words, not to stuff a page with every phrase you can think of. Finding those phrases is its own step, covered in keyword research. Matching the words a customer actually uses is a necessary condition for that customer to find the page at all.