Recent years has seen dramatic growth to the study of frictions that individuals experience, especially in their interactions with the public sector, creating both the potential for new research opportunities and conceptual confusion. We seek to head off the latter by providing, in one place, a definition, description of the development, and comparison of four dominant conceptions of frictions: ordeal mechanisms, red tape, administrative burden, and sludge. In particular, we discuss the four concepts' definition and use in terms of their objectivity, distributive effects, object and domain, and deliberate design. The paper helps researchers to understand the overlap and distinctions between these concepts, and the role of public administration in these different traditions. Comparisons of the different approaches' thinking also suggest opportunities for mutual learning.