A so called "bishop's mantle".
This kind of maille cape was used by military men during the 16th century, most famously by the German Landsknechts.
It is also part of Sir VIilheim's suit of armor in Dark Souls III.
[AMX-004 - QUBELEY CNIDARIA ASPECT]
The gentle edge of my body - the place where I end and you begin - at the point of precious human contact - that was where I cultivated an immaculate toxin