Plans for all-postal primaries for candidates in 200 seats before 2015, which are being reconsidered in light of the stalled boundary review process.

BBC: UK Politics

When light travelling through the core deviates from its course and hits the cladding, the boundary between the two acts as a mirror, and the errant light is reflected back into the core.

ECONOMIST: New-age crystals

The eerie light probably came not from the substance itself, but from the boundary between it and the glass layer below.

ECONOMIST: Combinatorial chemistry

In other words, the boundary between the supersonic and subsonic regions would do for sound waves what the event horizon does for light.

ECONOMIST: Black holes on a desktop: Dumb insolence | The