interstice

Short definition from Wiktionary

Noun

1. 1
   A small opening or space between objects, especially adjacent objects or objects set closely together, such as between cords in a rope, components of a multiconductor electrical cable or 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
   A small interval of time free to be spent on activities other than one's primary goal.