MOULD' (3 letters) The term MOULD ARRAY is a combination of two words. MOULD is a noun that refers to a hollow form or MATRIX in which a fluid or plastic substance is poured or pressed to give it a particular shape. MATRIX is a noun that refers to an arrangement of elements in rows and columns, often used to represent data or mathematical operations. Together, MOULD ARRAY can refer to a specific type of MATRIX that is used to create a particular shape or form.