It is the point at which particle motion stops for monatomic ideal gases. However, molecules will still vibrate.
All temperatures above absolute zero will cause particles in any material to move/vibrate slightly, as temperature gives particles Kinetic energy, according to the equipartition theorem for monatomic ideal gases:
#k_B# = Boltzmann's constant = #1.38065 times 10^-23 J//K# #T# = absolute temperature (Kelvin)
At absolute zero, #T = "0 K"#, so there is effectively no average kinetic energy of the molecules. (although the state of absolute zero is more of a concept as it has not yet been achieved). This means that particle motion ceases in monatomic gases.
Absolute zero is also the foundation for the Kelvin scale, as #"0 K" = -273.15^@ "C"# is the coldest that you can ever hope to get.