For most small businesses a conversion is a phone call, a form sent, a booking made or an order placed. A few more count depending on the business: a tap on the directions link, a menu opened, a quote request started.
Whatever it is, it is the moment a visitor becomes a customer or a lead, and it is the one number a website exists to move.
Conversion rate is conversions divided by visitors. If 1,000 people visit a site in a month and 20 of them call or send the form, the conversion rate is 2 percent.
A difference of a point or two sounds small until you do the math on a year of visitors, and the difference is usually not the business. It is the website: how fast it loads on a phone, whether the phone number is one tap away, whether the reviews are there, whether the next step is obvious.
That is why I measure before I change anything. Google Analytics with call and form tracking tells me where visitors come from, which pages they read, and where they leave. Those numbers, not a hunch about the home page, decide what gets fixed first.