The general definition of anxiety disorder is … simplified:
A person develops anxiety of various degrees, but there are no externally identifiable occasions for the anxiety.
Thus, a baseless anxiety, according to the ICD-10 definition:
“In these disorders, manifestations of anxiety are the main symptoms without being related to a specific environmental situation. Depressive and obsessive-compulsive symptoms, even some elements of phobic anxiety may be present, provided they are clearly secondary or less pronounced.”