building block

/B IH1 L D IH0 NG B L AA1 K/
noun
  1. 1

    A component that is part of a larger construction, such as a brick or a stone.

    โ€œCells are the building blocks of life.โ€

  2. 2

    A block made of wood or plastic that is used as a children's toy and can be stacked or joined to form a larger structure.

Source: https://en.wiktionary.org/wiki/building%20block