A card is considered named in game when a player has provided a description (which may include the name or partial name) that could only apply to one card. Any player or judge realizing a description is still ambiguous must seek further clarification.
Anytime a player names a card, it needs to be done in a way so everyone is aware of what card they are naming. If anyone believes they have not done so, they need to ask for further clarification
Players have the right to request access to the official wording of a card the can describe. That request will be honored if logistically possible.
The fact that most card-searching apps include Oracle text is made very relevant by this bit. Players will often request oracle text for cards they or their opponents are using in tournaments, and judges should be prepared to provide it. Several phone apps include complete, downloaded, searchable databases of every single card’s Oracle text, and these are by far the easiest way to quickly find and display it. As a general rule, if you can punch the info they give you into the search function and find a precise card, they’ve described it well enough. Saying “the green three drop that people play a lot in standard” or “The one-drop red burn spell” isn’t uniquely identifying a card, but saying “The white planeswalker from Magic: Origins” or “The take an extra turn card with Delve” is. If a card is revealed to a player, they do not need to know anything about the card to request Oracle text for it.
The official text of any card is the Oracle text corresponding to the name of the card.
Regardless of what the text on the card says, any sanctioned event must use the current Oracle text for each card, which can be found on Gatherer or pretty much on any phone app that you can search for cards on. If we didn’t use Oracle text, several old cards wouldn’t work with the game’s rules, several cards would be missing important errata, and the Portuguese printing for Stoic Rebuttal wouldn’t actually do anything.
Players may not use errors or omissions in Oracle to abuse the rules. The Head Judge is the final authority for card interpretations, and he or she may overrule Oracle if an error is discovered.
This may look like a clause that’s included just in case a card has a typo, but there have been cases where a Head Judge has overruled an oracle to prevent abuse. Wizards of the Coast is much more careful about the cards they print and the errata they make these days, but there have been high profile cases of a Head Judge overruling Oracle, notably the 1999 French Nationals and the Oracle text for Yawgmoth’s Will.