Secular stagnation is where economic growth is persistently negligible or very low. The first notable economist to talk about secular stagnation was Alvin Hansen, who argued in the late 1930s that economic growth in the US was low and would remain low due to declining population growth and declining technological innovation. The post-war baby and technological booms meant that people largely forgot about Hansen's theory. However, in the light of low economic growth and near-zero real interests which have persisted since 2008, Larry Summers and others have revived the secular stagnation hypothesis - click here and here. In the video below, Oxford's Kevin O'Rourke gives a lecture to the British Academy entitled "Economic Impossibilities For Our Grandchildren?" which addresses the secular stagnation hypothesis and prescribes various policies to address it. A working paper version of his lecture is available here.