  Using both fluid and kinetic descriptions, where repulsive forces between
near by atoms are included, we discuss the basic oscillations and waves of a
cloud of ultra-cold atoms confined in a magneto-optical trap. The existence of
a hybrid mode, with properties similar to both plasma and acoustic waves is
described in detail. Tonks-Dattner resonances for confined hybrid modes in a
spherical cloud are discussed and the prediction of a nonlinear coupling
between the dipole resonanc and the hybrid modes is considered. Landau damping
processes and quasi-linear diffusion in velocity space are also discussed.
