They're calling it Disease X. It's a mysterious illness circulating in a remote part of the Democratic Republic of Congo. Current figures: almost 400 cases and 79 deaths. International health authorities are monitoring.
Disease X is actually a concept. In academia, Disease X is covered in infectious disease focused courses, it is a placeholder concept referring to a pandemic pathogen which has not yet been characterized. Its purpose is to encourage proactive thinking and research about pathogens that could cause a pandemic. To see the term thrown around is pretty wild, but hopefully it's a bit of an overzealous or incorrect use of it. Not even sure if there's enough data available yet to classify it as Disease X, but it's Ro value is steadily on the rise, which is always concerning for a novel pathogen.