The black square hat worn by US and UK graduates and teachers.
Fast modeling. Enough for a distant view.
Thanks for your comment Artales :
"...Here in the UK it is jovially called a ‘mortar board’. My teachers used to wear one together with a gown on normal school days so it is not ‘undergraduate’ student apparel, we wore caps. ‘Graduate’ students qualify to wear one as a signifier of graduation..."