Complex sentence: Like a dipole antenna, a monopole has an omnidirectional radiation pattern; that is the radiation is equal in all azimuthal directions perpendicular to the antenna, but varying with elevation angle, with the radiation dropping off to zero at the zenith, on the antenna axis.
Split into simpler sentences: Like a dipole antenna, a monopole has an omnidirectional radiation pattern. That is it radiates equal power in all azimuthal directions perpendicular to the antenna, but the radiated power varies with elevation angle, with the radiation dropping off to zero at the zenith, on the antenna axis.