35/66 as a percentage is 53.03%. This value tells you how much of a whole the fraction represents when you look at it in terms of 100 parts.
The fraction 35/66 can be thought of as 35 pieces out of a total of 66 equal pieces. When you compare those pieces to a full set of 100, you end up with a little more than half, which is why the percentage is just over 50%.
In everyday use, you might see 53.03% on a report card, a budget, or a sports statistic. It gives a quick, easy‑to‑read picture of the same information that the fraction 35/66 provides.