Jeon refers to a dish that is thinly sliced, coated in flour or mung bean flour and beaten-up eggs, and pan-fried in oil.
The <Joseon Moosang Sinsik Yori Jebeop> states that jeon was a dish that was always served at all kinds of feasts and tables, from weddings, funeral rites, ancestral rites and birthdays, to large banquets and drinking parties. 
Let's take a look at the various ingredients used to make jeon.

Source·Reference. National Institute of Agricultural Sciences, Rural Development Administration 

A Different Transformation of Meat
Meat is an ingredient that has been widely used in making Jeon.
Donggeurangttaeng(meat fritter), which is made with minced meat and vegetables, is often served during ancestral rites, and yukjeon(pan-fried, battered beef), which is made with thinly sliced beef, is a traditional dish eaten at weddings and during holidays.  

Yukjeon(Pan-fried, Battered Beef)

Ingredients : 400 g beef, 100 g dry sticky rice powder
Meat marinade: 2 tbsp sweet soy sauce, 2 tbsp plum sauce(sugar), 1 tbsp cheongju, 1 tbsp chopped garlic, 1/3 tsp pepper, 1 tbsp sesame oil
How to make it
① Slice the beef into 1-2 mm thickness. 
② Remove the blood from the meat, and season it with meat marinade.
③ Coat the beef with sticky rice powder evenly. 
④ Coat the beef again with sticky rice powder.
⑤ Heat oil in a frying pan, and pan-fry the meat on both sides. 

Enhancing the Flavor of Fish
Jeon made by thinly slicing the fish was called eojeon.
When making eojeon, light white fish, such as flounder and pollack, was mainly used. Jeon, which uses plenty of oil to make and is rare in Korean food, added flavor to light fish. 

Dongtaejeon(Pan-fried, Battered Pollack Fillet)

Ingredients : 200 g pollack fillets, 1 egg, 4 tbsp flour, 1/2 tsp salt, a bit of pepper, 1 tsp chopped garlic, 2 tbsp oil 
How to make it
① Dry the pollack fillets with a kitchen towel.
② Sprinkle salt and pepper evenly on the front and back of the fillets.
③ Mix the egg, garlic, and salt well in a bowl.
④ Coat the fillets evenly with flour and with the egg mixture.
⑤ Heat oil in a heated pan, and pan-fry the fillets

With the Sea Flavor of Shellfish
Shellfish have also been loved for a long time as an ingredient for jeon. Many cookbooks from the Joseon Dynasty to the modern times introduce a variety of jeons brimming with the flavor of the seas, such as guljeon(pan-fried, battered oyster), saewoojeon(pan-fried, battered shrimps), jogaejeon(pan-fried, battered clams), etc.

Guljeon

Ingredients : 100 g oysters, 4 tbsp flour, 1 egg, a bit of water, 1 tbsp oil, 1/4 tsp salt, 
1 tbsp cooking wine, 1/4 tsp sesame oil, a bit of pepper
How to make it
① Wash the oysters in salt water, and drain them in a colander.
② When it is drained, season with salt, cooking wine, sesame oil, and pepper.
③ Coat the oysters in flour evenly, and dip them in the beaten egg.
④ Heat oil in a pan, and pan-fry both sides until golden brown.

Another Way to Enjoy Vegetables
Vegetables seem to have played a major role in making the types of jeon infinite. A variety of vegetables were used as jeon ingredients to make potato jeon, green onion jeon, zucchini jeon, chili pepper jeon, perilla leaf jeon, golden oak mushroom jeon, etc.

Pajeon(Green Onion(Scallion) Pancake)

Ingredients : 120 g scallions, 50 g onion, 1/2 red chili, 80 g flour, 100 ml water, 1/2 egg, salt, oil
How to make it
① Mix the flour, salt, and water well. 
② Beat the egg in a bowl. 
③ Cut the scallions into 15-cm long slices, onion, 5-cm long slices, and chili, 2-cm long slices. 
④ Heat oil in a pan, spread the dough well, and add the scallions. 
⑤ Sprinkle the sliced onion and red chili on top of the scallions.
⑥ When the batter is half-cooked, sprinkle the egg evenly over it, and flip it over to cook until golden brown.