The way in which you might arrange your hand into suits, expressed as the number of cards in each suit. For example: a 5-4-3-1 shape means you have a five-card suit, a four-card suit, a tripleton and a singleton.
If there are dashes in between the numbers, this is likely to indicate a specific shape. For example, a 2-4-6-1 shape means two spades, four hearts, six diamonds and one club.
Another name for shape is the hand’s ‘pattern’ or ‘distribution’.