In the four-level hierarchy that characterizes a MoStack the cards are the third level.
What in other data management programs is called records or entries is called cards in MoStacks, in analogy to index cards, as explained in chapter Concepts.htm.
Each card belongs to one and exactly one background that decides which fields and controls go where on the card. Currently it is not possible for a card to hold card-specific extra fields and controls beside the ones from the background, but that's a possible future enhancement.
MoStacks itself has no limit for the number of cards per background or per stack as a whole, but as MoStacks holds everything about the stack in memory, the amount of phone main memory available to the MoStacks application ultimately limits the size of the stack.
Beside the fields that hold the data cards have another important aspect: They have names that identify them, as explained in chapter Card Names