White Leghorn - Weighing about 4 lbs at maturity, these birds start laying at 4 1/2 to 5 months, and continue laying 10 to 12 weeks longer than most other good layers. The White Leghorn is a healthy productive breed of hen with high resistance to disease.
There are three consumer grades for eggs: U.S. Grade AA, A, and B. The grade is determined by the interior quality of the egg and the appearance and condition of the egg shell. Eggs of any quality grade may differ in weight (size).
U.S. Grade AA eggs have whites that are thick and firm; yolks that are high, round, and practically free from defects; and clean, unbroken shells. Grade AA and Grade A eggs are best for frying and poaching where appearance is important.
U.S. Grade A eggs have characteristics of Grade AA eggs except that the whites are "reasonably" firm. This is the quality most often sold in stores.
U.S. Grade B eggs have whites that may be thinner and yolks that may be wider and flatter than eggs of higher grades. The shells must be unbroken, but may show slight stains. This quality is seldom found in retail stores because they are usually used to make liquid, frozen, and dried egg products.
More information from the USDA - https://www.ams.usda.gov/grades-standards/shell-egg-grades-and-standard
Size tells you the minimum required net weight per dozen eggs. It does not refer to the dimensions of an egg or how big it looks. While some eggs in the carton may look slightly larger or smaller than the rest, it is the total weight of the dozen eggs that puts them in one of the following classes:
About your egg...
Cage Free Housing
This type of housing provides a safe living space for the hen, free from predators. The hens have ready sources of food and water.
Hens are able to roam and fly within the barn, and can express their natural behaviors such as roosting and dust bathing. Hens are provided with private nesting space for laying their eggs.
Eggs are collected daily and processed and packed within 24 hours of being laid - except for public holidays, when the eggs may be packed 36 to 48 hours after being laid.
See this article from UC Davis for more information on hen housing - http://www.caes.ucdavis.edu/news/articles/2015/04/examining-the-effects-of-hen-housing
About your egg...
The veterinary care for Young birds (chicks and pullets) includes close monitoring for any sign of disease or parasites, and their growth rate is checked for consistency and uniformity. They are fed diets rich in calcium, vitamins and other minerals, and their feed and water consumption is monitored closely. This close attention to their health assures the flocks maintain a positive temperament with low mortality rates, have high egg yields, and produce excellent quality protein nutrition in strong, durable shells.
Birds are not molted.
The flock is vaccinated. Vaccination is globally proven to be the most successful way to limit occurrences of salmonella occurring in eggs derived from commercial flocks. In addition, laying hens receive vaccinations against diseases that are common or that are difficult to eradicate, such as Marek's disease, infectious bronchitis, and fowl pox.
The flock is antibiotic free.