To be removed from play (also called RFG or removed from game) is a term used to describe when a card is removed from the Duel by another card's effect. Once a card is removed this way, it cannot re-enter the current duel, except by a card that specifically allows it, such as "Return from the Different Dimension".
Originally, there were not many cards which could remove other cards from play, with some of the first being "Nobleman of Crossout" and "Nobleman of Extermination". However, over time, removal has become a popular theme, with several cards to go with it (Chaos and D.D. (Different Dimension) cards, for example.) And, in turn, more cards were created to bring them back, such as "D.D.M. - Different Dimension Master", "Dimension Fusion", "Dimension Explosion" and "Burial from a Different Dimension".
Removal is good for breaking strategies, especially when combined with a card like "Fiber Jar", which reunites every player's hand, Deck, Field Contents, and Graveyard, into a new Deck, but doesn't combine cards removed from play. Combined with monsters like "Gren Maju Da Eiza", "Golden Homunculus" or any in the "Helios - The Primordial Sun" series can give a player some of the highest attack powers in the game.
Since currently, many decks rely on the Graveyard, Decks that rely on the effects of "Dimensional Fissure", "Macro Cosmos" and "Banisher of the Radiance", along with "D.D. Survivor" have grown in power. Being able to shut down an opponents Graveyard, plus having an 1800 ATK monster in Survivor that keeps returning itself every time it's removed from play while face-up for as long as the removal card is active, have shown themselves to be powerful decks.
The Removed from Play Zone can be placed anywhere on the table, as it has no actual place in the game. However, most typically it is placed above or to the right of the Graveyard Zone, placed face down beneath the Graveyard, or just under the field (right in front of the player).