  QFP wave trains in the corona have been studied intensively in the past
decade, thanks to the full-disk, high spatiotemporal resolution, and
wide-temperature coverage observations taken by the SDO/AIA. In AIA
observations, QFP wave trains are seen to consist of multiple coherent and
concentric wavefronts emanating successively near the epicenter of the
accompanying flares; they propagate outwardly either along or across coronal
loops at fast-mode magnetosonic speeds from several hundred to more than 2000
km/s, and their periods are in the range of tens of seconds to several minutes.
Based on the distinct different properties of QFP wave trains, they might be
divided into two distinct categories including narrow and broad ones. For most
QFP wave trains, some of their periods are similar to those of quasi-periodic
pulsations (QPPs) in the accompanying flares, indicating that they are probably
different manifestations of the same physical process. Currently, candidate
generation mechanisms for QFP wave trains include two main categories: pulsed
energy excitation mechanism in association with magnetic reconnection and
dispersion evolution mechanism related to the dispersive evolution of
impulsively generated broadband perturbations. In addition, the generation of
some QFP wave trains might be driven by the leakage of three and five minute
oscillations from the lower atmosphere. As one of the new discoveries of SDO,
QFP wave trains provide a new tool for coronal seismology to probe the corona
parameters, and they are also useful for diagnosing the generation of QPPs,
flare processes including energy release and particle accelerations. This
review aims to summarize the main observational and theoretical results of the
spatially-resolved QFP wave trains in extreme ultraviolet observations, and
states briefly a number of questions that deserve further investigations.
