  Amidst widespread reports of digital influence operations during major
elections, policymakers, scholars, and journalists have become increasingly
interested in the political impact of social media 'bots.' Most recently,
platform companies like Facebook and Twitter have been summoned to testify
about bots as part of investigations into digitally-enabled foreign
manipulation during the 2016 US Presidential election. Facing mounting pressure
from both the public and from legislators, these companies have been instructed
to crack down on apparently malicious bot accounts. But as this article
demonstrates, since the earliest writings on bots in the 1990s, there has been
substantial confusion as to exactly what a 'bot' is and what exactly a bot
does. We argue that multiple forms of ambiguity are responsible for much of the
complexity underlying contemporary bot-related policy, and that before
successful policy interventions can be formulated, a more comprehensive
understanding of bots --- especially how they are defined and measured --- will
be needed. In this article, we provide a history and typology of different
types of bots, provide clear guidelines to better categorize political
automation and unpack the impact that it can have on contemporary technology
policy, and outline the main challenges and ambiguities that will face both
researchers and legislators concerned with bots in the future.
