Interstice

noun

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. A fragment of space.
3. An interval of time required by the Roman Catholic Church between the attainment of different degrees of an order.
4. (by extension) A small interval of time free to be spent on activities other than one's primary goal.