  Online forums provide rich environments where users may post questions and
comments about different topics. Understanding how people behave in online
forums may shed light on the fundamental mechanisms by which collective
thinking emerges in a group of individuals, but it has also important practical
applications, for instance to improve user experience, increase engagement or
automatically identify bullying. Importantly, the datasets generated by the
activity of the users are often openly available for researchers, in contrast
to other sources of data in computational social science. In this survey, we
map the main research directions that arose in recent years and focus primarily
on the most popular platform, Reddit. We distinguish and categorise research
depending on their focus on the posts or on the users, and point to different
types of methodologies to extract information from the structure and dynamics
of the system. We emphasize the diversity and richness of the research in terms
of questions and methods, and suggest future avenues of research.
