Each web page has a title set in its code, separate from the big heading you see on the page itself. Google usually uses it as the blue clickable line in search results, and browsers show it on the tab.
A good one says what the page is about and where, in plain words, with your business name at the end. Google cuts off titles that are too wide for the results page, so the useful part should come first; somewhere around 50 to 60 characters is a sensible rule of thumb.
Google can and does rewrite titles it thinks are unhelpful, stuffed with keywords or do not match the page, so writing an honest, specific one is the best way to keep yours.
The title is often the first thing a potential customer reads about you. ‘Home’ or ‘Welcome’ tells them nothing; ‘Boiler Repairs in Exeter | Same-Week Visits | Smith Heating’ tells them you do what they need, where they need it.