The chapter defines the meaning of online silence, explains how it occurs in virtual classroom settings and unpacks the phenomenon as learning engagement or the lack of it in cognitive, social, emotional, and technological dimensions. Online silence is an unsettled, under-theorised construct without a universal definition but varies according to context and educators’ various levels of patience when waiting for learner response. The author argues that online silence represents both a barrier to and a condition for learning efficacy. Drawn extensively from the research discourse on the occurrence and absence of learner participation, the discussion outlines how silence pervades the digital educational environment. The discussion first defines the meaning of online silence and examines how online instruction provokes silence. Secondly, the dynamic of silence is unpacked concerning both learning engagement and learning disengagement in cognitive, social, emotional, and technological dimensions. Thirdly, it is argued that online silence exhibits two opposing impacts by being both a barrier to and a condition for learning efficacy. The chapter embraces online silence in language learning and in subject-content education considering that learners need to develop not only language proficiency but also knowledge and skills for real-world communication.