The harvest date is when the cannabis plants were cut down, and the pack (or packaging) date is when the product was sealed in its package. Many labels show one or both.
These dates help you judge freshness. Flower gradually loses terpenes, the compounds behind smell and taste, after harvest, and over a long time some THC can break down into CBN. Fresher flower usually has stronger aroma and better flavor, though a good cure takes a few weeks after harvest, so "just harvested" is not the goal either.
There is no exact shelf life, because storage makes a huge difference. Flower kept in an airtight container, in a cool, dark place, holds up far better than flower left in a warm car or in direct sunlight. Concentrates, edibles and carts have their own timelines; edibles may have a best-by date.
When shopping, compare dates between similar products, and ask our staff what is newest. At home, store your products sealed, cool and dark, and keep them away from children and pets.