non-stop, at a stretch, voraciously, in one go
in binges, heavily (of drinking)
ravenously, predatory, rapaciously, voraciously
Он чита́ет запоем.
He reads voraciously.
Читывавший книги запоем, он знал наизусть множество стихов.
Having read books voraciously, he knew countless poems by heart.
