Concept art is the process of drawing up ideas and developing creatures, objects or worlds, concept art helps artists create a large number of ideas, then putting the best and most fitting together to make a well designed asset that will be used in a game. Concept art has many misconceptions, with companies putting high quality art and labelling it "concept art" they glorify lies, the realistic thing is that concept art (especially early stages of it) tends to be a bunch of loose sketches, drawn quickly to convey an idea instead of look nice.
Concept art can be broken down into 3 stages.
-Exploration
Exploration depicts an artist loosely sketching out ideas, brainstorming to create several distorted versions of the same basic idea. This part of concept art is mainly internal and stays that way as unused ideas can be recycled in he future to create other characters. This artwork is commonly 'remastered' if it is to be released to the public, this is done to make the art team and the company behind them look more posh and impressive, this is probably what happened to the example below.
Picture from Borderlands 2 - Art by Kevin Duc
-Approval
Approval is the part of Concept art creation where the artist will present the drawing to higher ups and get their opinions, they will get told which sketch to develop further and any extra things that should be tweaked or added. In the example you can see many reference pictures next to the drawing of the character, this will be used as a guide for 3D modellers and other parts of the team, this can be seen with the plagiarism of images, use of images in the drawing itself (look closely at the medallion, its taken directly from the picture, not drawn) and the flipping of the drawing to create the base for the back of the character. This may be polished up and fixed of these problems then released in the concept art book.
Uncharted 2: Among Thieves - Art by Hong Ly
-Promotion
This is the final step of the Concept art possess, at this point the character's design has been desired on and perfected, a new piece of art is created to build hype for the character and show them off to the public, this artwork is highly detailed, puts the character in an exciting environment and has all the attention on them. The artwork below depicts Yveltal, the legendary from the Y game, towering over a destroyed and ruined town going up in flames, the lighting on the character and the intimidating pose are created this way to make the player eager to play and capture Yveltal so they could use him in battle, as he is presented as this strong and mighty god.
Pokemon X & Y - Art by Ken Sugimori
Sources:
http://www.randbin.com/what-is-concept-art/
https://www.artstation.com/artwork/kmVE6
https://www.artstation.com/artwork/nv2DX
https://www.videogamesartwork.com/games/borderlands-2/tundra-building-exploration-zone-1
http://howtonotsuckatgamedesign.com/2014/02/lets-get-real-concept-art/
https://www.reddit.com/r/pokemon/comments/1mbseb/some_pretty_epic_official_artwork_of_yveltal_and/
