This is an aerial view of a brick wall with a diagonal buttress. Therefore, it is the noun diagonal buttress.
Illustrative Text Reference:
Mohenjo-daro: Seal: M-372 a: Jagat Pati Joshi and Asko Parpola, 1987: Corpus of Indus Seals and Inscriptions: Volume 1: Page 93: Collections in India: Suomalainen Tiedeakatemia.
Image Credit:
Indus Script Sign Number 1438: List of Sign Variants: Iravatham Mahadevan, 1977: The Indus Script: Texts, Concordance and Tables: The Director General Archaeological Survey of India.