A visit to a topic. Duplicate visits from the same user are counted after a 8 hour interval. A user is either a logged in user or an IP address for anonymous visitors. The 8 hour interval can be changed with the site setting topic view duration hours.
@Kris very useful information, thanks. It means, though, that using views as a gauge of implicit support is more limited than I imaged. Although I guess I could seek explicit support by running a poll or even just asking for likes. Thanks again for your reply. R