Samsung has filed for a trademark in the EU for the U Flex brand as of yesterday, as the application date notes that it was filed on March 7th. There isn't any detail in the trademark application about what U Flex will be, but current speculation is that it may be the name of a new pair of headphones that Samsung could be developing and is looking to bring to market in the future. More specifically it's thought that U Flex may be a new pair of wireless headphones from Samsung's Level series, though there is still no actual detail that can confirm this just yet.
With that said, the "U" may be referring to the series model of headphones just as the U does in Samsung's Level U headphones, while Flex may be referring to a specific trait of the headphones themselves, perhaps detailing that they have a flexible build quality to them. If this is the case then the U Flex could be aimed at fitness enthusiasts, though they could really just be for the general consumer as well. Truthfully, without much information other than the name of the brand it's mostly impossible to tell what the headphones will be like, but with Unpacked coming up at the end of this month there is always a chance that Samsung may announce more details during the event alongside the Galaxy S8 and the Galaxy S8 Plus.
What is known is that these are a pair of headphones, it's just not clear what sorts of features they will have or if they will even be part of the Level series. The trademark application also lists that they will have Bluetooth technology inside of them so they will be wireless, although there is no information on which version of Bluetooth Samsung will be planning to use with the U Flex headphones. It's also unclear if U Flex will end up as part of the name once these reach production and are ready to hit store shelves. If Samsung ends up announcing these later on this month, then at that time they may also share information on pricing and availability.