If you describe something or someone as first-class, you mean that they are extremely good and of the highest quality.

You use first-class to describe something that is in the group that is considered to be of the highest standard.

First-class accommodation on a train, aeroplane, or ship is the best and most expensive type of accommodation.

In Britain, first-class postage is the quicker and more expensive type of postage. In the United States, first-class postage is the type of postage that is used for sending letters and postcards.