Name and reason for space between pixels on an LCD display
The up-voted and accepted answer is not even wrong.  It's pure guessing.

There are no individual pockets in LCD panels.  They are two parallel glass plates with special films applied.  The plates are held apart with tiny beads (PMMA or Glass)- on the order of 10's of microns.

When two adjacent pixels are set at different voltage levels the LC between the pixels are at an indeterminate state due to the ambiguous fields.  In the industry these are called disinclination lines.  To hide these lines a black mask is applied between the filters and to increase contrast.

Disinclination lines do not appear in every LCD technology but the black mask increases perceived resolution and display "crispness".