A standard meld is a set of either 3 or 4 cards where there is one metro line that is common to all cards. In the example below, Caledonian Road, Finsbury Park and Acton Town are all on the Piccadilly Line, so can be melded together. Note that as Finsbury Park is a connection station and is also on the Victoria line, it could also be melded with 2 or 3 other Victoria line stations. Similarly Acton Town could belong to a District line meld. However, a card can only belong to one meld at a time.
The cards are designed with line symbols in the top left/bottom right corners so that the meld can be displayed more compactly with the cards overlapping, as shown in the lower part of the image below.
It is possible to add another Piccadilly Line station card to the meld below as standard melds can have either 3 or 4 cards.
There is a special multi-line meld of either 4 or 5 cards, where every station cards is a single-line card, and all the cards represent different lines. In the example below Lambeth North is on the Bakerloo, Oval is on the Northern, Fulham Broadway is on the District and Bermondsey is on the Jubilee line. None of the stations are connection stations.
It is possible to add a 5th card to this meld as long as it is another single line station and is on a different line from the 4 other cards.
The Inspector cards count as wild cards and can be used in any meld as appropriate to make that meld valid.