"Fabergé egg" refers to any of thousands of jeweled eggs crafted by the House of Fabergé, a jeweler in St. Petersburg, Imperial Russia, between 1885 and the dissolution of the firm in 1918 following the Russian Revolution. The eggs originated as gifts for Easter. Most Fabergé eggs were quite small, and were typically worn on necklaces as charms. However, the House of Fabergé produced around 65 very large jeweled eggs, of which 57 survive today. Most of these (around 50) were produced for the Russian Tsars. These "Imperial" eggs are the most famous, and are the eggs most commonly thought of when the term "Fabergé egg" is used nowadays. Each Imperial egg is unique and has a special name.
Because of the rarity and fine craftsmanship of these large eggs, Fabergé eggs are incredibly valuable and have become an iconic exemplar of a fantastically expensive work of art. They almost never come on the market, but when they do, they can be expected to sell for millions of dollars each.