Melds are a way of scoring and seeing your progress in Mine Things. A meld is a collection of items that is combined together. When you make a meld the items have to all be in your home city, and you have to have every item in the meld (no partial or incomplete melds). Each meld is worth 1 meld point, which is the way of showing how many melds you have. Melds have different colours, depending upon the rarity of items used in the meld. Different colours do not affect the amount of meld points you get.
Currently melds have no use except for extending your battery by another hour, but that will change soon.