  For almost 20 years the physical nature of globally propagating waves in the
solar corona (commonly called "EIT waves") has been controversial and subject
to debate. Additional theories have been proposed over the years to explain
observations that did not fit with the originally proposed fast-mode wave
interpretation. However, the incompatibility of observations made using the
Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric
Observatory with the fast-mode wave interpretation was challenged by differing
viewpoints from the twin Solar Terrestrial Relations Observatory spacecraft and
higher spatial/temporal resolution data from the Solar Dynamics Observatory. In
this article, we reexamine the theories proposed to explain "EIT waves" to
identify measurable properties and behaviours that can be compared to current
and future observations. Most of us conclude that "EIT waves" are best
described as fast-mode large-amplitude waves/shocks that are initially driven
by the impulsive expansion of an erupting coronal mass ejection in the low
corona.
