In the context of medicine and pathology, the term "hallmark" refers to a distinctive or characteristic feature or sign that is commonly associated with a particular disease, condition, or phenomenon. Hallmarks are often used to aid in the identification, diagnosis, or classification of a specific medical condition.

Hallmarks are typically based on prominent and consistently observed features that are unique or highly indicative of a particular disease or condition. They can be clinical signs, symptoms, laboratory findings, imaging abnormalities, histopathological features, or molecular markers.

For example, in Alzheimer's disease, the presence of neurofibrillary tangles, amyloid plaques, and certain cognitive impairments are considered hallmarks of the disease. These features help differentiate Alzheimer's disease from other types of dementia and contribute to its diagnosis.

Hallmarks can also be used to describe broader phenomena. For instance, in cancer biology, the "hallmarks of cancer" refer to a set of distinct capabilities or characteristics acquired by cancer cells that enable their growth, invasion, and resistance to treatments. These hallmarks include sustained cell proliferation, evasion of cell death, angiogenesis (formation of new blood vessels), and genomic instability, among others.

Hallmarks serve as important diagnostic, prognostic, and therapeutic markers in medicine and provide a framework for understanding the underlying mechanisms and manifestations of various diseases and conditions.