  Chimera states, states of coexistence of synchronous and asynchronous motion,
have been a subject of extensive research since they were first given a name in
2004. Increased interest has lead to their discovery in ever new settings, both
theoretical and experimental. Less well-discussed is the fact that successive
results have also broadened the notion of what actually constitutes a chimera
state. In this article, we critically examine how the results for different
model types and coupling schemes, as well as varying implicit interpretations
of terms such as coexistence, synchrony and incoherence, have influenced the
common understanding of what constitutes a chimera. We cover both theoretical
and experimental systems, address various chimera-derived terms that have
emerged over the years and finally reflect on the question of chimera states in
real-world contexts.
