Does this status mean it has been sent to referees? Or is could it still be desk rejected?
Under review implies it has been sent out for peer review and has passed the initial check. T & F primarily uses ScholarOne Manuscripts but also have their own electronic submission system. There may be slight differences between these but I would think they are set up similar to each other. I am familiar with the ScholarOne system.
From my experience, this status means that the manuscript has passed the in-house review and has been sent out to the reviewers.