Packaging is full of terms that sound official but aren't always regulated the same way. Here's what actually stands behind each one.
Organic
A legally defined term. Hens are fed certified organic feed, kept at a lower stocking density than any other system, and must have outdoor access with pasture rotation. See the full organic eggs page.
Free-range
A legally defined term. Hens must have regular daytime access to the outdoors. See the full free-range eggs page.
Barn
A legally defined term. Hens are housed indoors with more space than a cage system, but with no outdoor access. See the full barn eggs page.
Cage / enriched colony
A legally defined term. Modern UK cage systems are "enriched" cages -- required to include perches, nesting areas, and a minimum space per hen, unlike the old battery cages they replaced. See the full cage eggs page.
Pasture-raised
Unlike the four terms above, "pasture-raised" has no fixed legal definition in the UK. It's used as a marketing term, sometimes to describe eggs from smaller-scale or higher-welfare free-range systems, but there's no single standard behind it the way there is for organic or free-range.
Corn-fed
A description of diet, not welfare or housing. "Corn-fed" just means the hens' feed included a higher proportion of corn (often reflected in a deeper yolk colour) -- it says nothing on its own about whether the hens were caged, barn-reared, or free-range. It's layered on top of one of the four main categories, not a replacement for one.
Class A / Class B
The official freshness and quality grading for eggs. Class A eggs are naturally clean with an intact shell and are what you buy as whole eggs in shops. Class B eggs don't meet that standard and are broken out and pasteurised for use in egg products rather than sold whole.
Best before
The date stamped on UK eggs (never "use by") -- by law, no more than 28 days after the egg was laid. It's a quality marker, not a hard safety cut-off. More on this in our storage & freshness guide.
Producer code
The full stamped code (e.g. 1UK12345) that this site reads -- farming method, country, and producer ID. See what are the codes on eggs?
Lion Mark
A separate food-safety certification (salmonella-vaccinated hens, full traceability), not a farming method. See what the Lion stamp means.
Sources: gov.uk -- egg marketing standards; egginfo.co.uk; The Humane League UK -- poultry label explainer.