In the game, "determination" usually appears in the form of yellow flash (save point), which can reply to the protagonist's HP and save the game data so that the player can return to the latest archive when restarting the game or dying.
Extended data
In the game, under certain conditions, Flowey will also introduce the meaning of "determination" at the exit of the ruins, which also implies that Flowey also has determination. At the end of the first neutral route, Flowey will absorb six human souls to become Omega Flowey and seize the player's file, which proves that the strength of determination can affect the ownership of the file.
"Determination" is a powerful force unique to the human soul, but monsters in extreme cases can also produce "determination" on their own.
After the blood volume of the neutral route Undyne returns to zero, Undyne will persist for a period of time (because the body can't hold too much "determination") and melt and die.