Use of the term "upcoming" for milestones is inconsistent
In the milestones page, we add an "Upcoming" label to milestones that have start dates in the future. This is based on: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/models/concerns/milestoneish.rb#L69
For filtering milestones (in the filter bar and board filters), we define "Upcoming" as the next milestone that is going to be due. This is based on: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/app/models/milestone.rb#L151