We have a two-word title on our hands, gang, so let's tackle them one at a time. First up is "Binsey," a village in central England not too far from Oxford, where Gerard Manley Hopkins went to college. It sits on the Thames river (the one that runs through the middle of London) and looks a lot like you would expect an idyllic English country village to look, even today. That means plenty of meadows and plenty of trees.
This leads us to the title's second word: "Poplars." As far as trees go, a poplar is a pretty snazzy one. It's tall and slender, with lots of shimmering leaves that look like they're dancing when the wind blows. Poplars also tend to grow together in small groups. They're both beautiful to look at and fun to be around.
The poem's title, then, gives us a pretty peaceful where ("Binsey") and a pretty beautiful what ("Poplars"). That makes things all the more depressing when, as soon as we leave the peaceful scene of the title, we learn in the epigraph that it's all been destroyed. Talk about a set-up. The title announces the poem's setting and subject (check out "Setting" for more), but it also serves as a reminder to the reader about exactly what's been lost, thanks to the handiwork of some thoughtless humans with axes. Way to ruin Nature, guys.