Any time you see the description "artificial" in front of a bid, it means that the suit being named is not necessarily a suit that the bidder possesses.
For example, if the auction begins: 1NT-2 by a partnership, the 2 bid is Stayman. What is the definition of 2? It is artificial (there's that word) and inquiring about opener's majors. Does it show clubs? Does it say anything about clubs? Of course not. The Stayman bidder might have a VOID in clubs! He might have 6 cards in clubs. Probably something in-between. The point is that the bid is artificial because even though the bidder is naming CLUBS with his bid, he is not attempting to make clubs trump and is saying nothing about his number of clubs.
Even a double can be artificial. For example, many players use a double of a strong 1NT opening to say "I have a 1-suited hand." This would be considered artificial (as opposed to a traditional penalty double of 1NT). A support double is another type of artificial double.
There are many artificial bids in bridge. Aside from Stayman, other common ones are Jacoby Transfers and the response to 4NT Blackwood -- such as 5 to show 2 aces. Obviously, that bid says nothing about wanting to make hearts the trump suit, so it is artificial.
Most conventions employ the use of artificial bids and require good memory by both partners. Doubles of such bids are typically lead-directing.
With the exception of Stayman, most artificial bids need to be either alerted or announced. Even Keycard Blackwoood gets "alerted", although that particular alert happens AFTER the end of the auction. This is sometimes called a "slow alert".
Last updated: December 2020