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_(avg)=3/2k_BT# #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.
Absolute zero is the temperature at which enthalpy and entropy of ideal gas reaches zero.
In Kelvin scale this temperature is taken as