Egg explains

https://pokemongo.fandom.com/wiki/Pok%C3%A9mon_Eggs

https://www.imore.com/how-to-hatch-eggs-pokemon-go

If you enable Adventure Sync, every week you can potentially earn two Eggs. These Eggs look like 5 KM and 10 KM Eggs, but the contents are different.

There are seven kinds of Pokémon Eggs in Pokémon Go:

• 2 KM Eggs with green spots.
• 5 KM Eggs (standard) with yellow spots.
• 5 KM Eggs* (Weekly Fitness 25 KM) with purple spots.
• 7 KM Friend Eggs that are yellow with pink spots
• 10 KM Eggs (standard) with purple spots.
• 10 KM Eggs* (Weekly Fitness 50 KM) with purple spots.
• 12 KM Strange Eggs with red spots   (Defeat Grunt Team Leader)

Note: Weekly Fitness Reward Eggs are visually identical to the standard 5 KM and 10 KM Eggs received from Pokéstops but have a much smaller pool of potential Pokémon.

5km eggs, 1194 stardusts,   12 candy

10km eggs, 2880 stardusts, 28 candy

10km eggs, 1972 stardusts, 19 candy

The following Pokémon are now hatching from Strange Eggs: Larvitar, Absol, Sandile, Scraggy, Trubbish, Pawniard, Vullaby, and Deino.

Different Pokémon are hatching from 2 km, 5 km, and 10 km Eggs. Please note that Pokémon that appear in the wild only in specific regions will hatch only from Eggs obtained in those regions.

The following Pokémon are now hatching from 2 km Eggs: Zubat, Poliwag, Cubone, Magikarp, Mareep, Wooper, Snubbull, Volbeat, Illumise, Wailmer, Swablu, Buizel, Buneary, Snivy, Tepig, Oshawott, and Minccino.

//Gastly from 2km eggs.

The following Pokémon are now hatching from 5 km Eggs: Machop, Farfetch’d, Seel, Voltorb, Lickitung, Kangaskhan, Tauros, Eevee, Pineco, Heracross, Corsola, Ralts, Aron, Torkoal, Feebas, Tropius, Clamperl, Relicanth, Mime Jr., Chatot, Hippopotas, Carnivine, Pansage, Pansear, Panpour, Pachirisu, Blitzle, Roggenrola, Maractus, Gothita, Solosis, and Bouffalant.

//Lavitar from 5km eggs

The following Pokémon are now hatching from 10 km Eggs: Shinx, Gible, Riolu, Audino, Timburr, Darumaka, Sigilyph, Emolga, Ferroseed, Klink, Elgyem, Litwick, Axew, Golett, and Rufflet.