Interpretation of the pole of a transfer function of a vibrating platform
As @jDAQ said, poles are the roots of the characteristic equation.

But a pole can take a real value or come as a complex pair, and your response plot is for a sine wave sweep -- and in the Laplace (s) domain the only frequencies in a sine wave are \$\pm j \omega\$.

A good physical interpretation of a transfer function such as \$H(s) = k/(s + a)\$ is that the system will have a strong response to sine waves at frequencies below \$\omega = a\$, medium at \$\omega = a\$ (strictly speaking, at half power), and diminishing response above.  Another one is that the system has a time-domain response containing the exponential \$e^{-at}\$.  Both of these are consistent with one another -- they're just two different ways of looking at the same problem.