Japanese philology; Japanese linguistics
Academic field studying the Japanese language, often with a historical and traditional focus. In modern contexts, 日本語学 is sometimes preferred for a more descriptive, synchronic approach.
He is majoring in Japanese linguistics at university.
From the perspective of Japanese philology, this expression is old.
言語学 is general linguistics, not limited to Japanese. 国語学 is specifically the study of the Japanese language.
Compound of 国語 (national language) and 学 (study, -ology). The term reflects the traditional view of Japanese as the national language of Japan.