12/51 as a percentage is 23.53%. This number tells you how much of a whole 12 parts out of 51 represent when you look at it on a scale of 100.
The fraction 12/51 can also be thought of as a part of a group. If you have 51 items and you pick 12 of them, you are taking about a quarter of the whole set. The decimal form of the fraction is 0.2353, which directly corresponds to the percentage above.
Knowing the percentage makes it easy to compare with other values. For example, 23.53% is close to one‑fourth (25%) but a little smaller, so you can quickly judge that 12 out of 51 is just under a quarter of the total.
