C90 or C-90 may refer to:
==Science and technology== Multiple myeloma and malignant plasma cell neoplasms (ICD-10 code) Caldwell 90 (NGC 2867), a planetary nebula in the constellation Carina C, the conventional electrical unit for the coulomb C90 audio cassette, a blank audio cassette in the very popular 90 (2 x 45) minute length
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).