An alphabet or script that has only one case — no distinction between uppercase and lowercase letters.
Definition
A unicameral alphabet is one that has only a single case of letters, with no distinction between uppercase and lowercase forms. Arabic, Hebrew, and many Indic scripts are unicameral by nature. In the Latin tradition, unicameral design is a deliberate typographic choice — some modern typefaces offer only one case (typically lowercase forms used at all sizes) to achieve a uniform texture. The term contrasts with bicameral, which describes scripts like Latin and Greek that use two cases. Unicameral typography can produce a distinctly modern, even texture but sacrifices the hierarchical and syntactic signals that capital letters provide.
Source
No access — Robert Bringhurst — p. 346:
Having a single alphabet, without separate upper and lower case.