  We uncover the interlayer shear mode of multi-layer graphene samples, ranging
from bilayer-graphene (BLG) to bulk graphite, and show that the corresponding
Raman peak measures the interlayer coupling. This peak scales from~43cm-1 in
bulk graphite to~31cm-1 in BLG. Its low energy makes it a probe of near-Dirac
point quasi-particles, with a Breit-Wigner-Fano lineshape due to resonance with
electronic transitions. Similar shear modes are expected in all layered
materials, providing a direct probe of interlayer interactions
