h28

H28 is a designation used in multiple domains; there is no universally accepted definition. Its meaning depends on context.

In science, if used as a hydrogen isotope notation H-28, it would denote hydrogen with mass number 28. No stable or confirmed isotopes of hydrogen with mass number 28 have been observed; such a hypothetical nucleus would be highly unstable and decays rapidly, if it could form.

In transportation and industry, h28 (lowercase h or capital H) is commonly used as an alphanumeric code to label routes, models, or products. The exact meaning varies by manufacturer, transit agency, or document; there is no universal standard attached to h28.

In other contexts, h28 may appear as a version or build identifier in software, hardware, or archival catalogs. Without context, the code provides little information beyond being a label.