Equatorially trapped waves

From Glossary of Meteorology

equatorially trapped waves

Planetary waves propagating parallel to the equator, the meridional structures of which are trapped in the vicinity of the equator.

Included are equatorial Kelvin waves, Rossby waves, mixed Rossby–gravity waves, and gravity waves. The equatorial trapping is due to the variation of the Coriolis parameter and the fact that the parameter itself is zero at the equator.
See also equatorial waveguide.