interstice

/ɪnˈtɜː.stɪs/
noun
  1. 1

    A small opening or space between objects, especially adjacent objects or objects set closely together, as between cords in a rope or components of a multiconductor electrical cable or between atoms in a crystal.

  2. 2

    A fragment of space.

  3. 3

    An interval of time required by the Roman Catholic Church between the attainment of different degrees of an order.

  4. 4

    (by extension) A small interval of time free to be spent on activities other than one's primary goal.

Source: https://en.wiktionary.org/wiki/interstice