Is there a name for this hair pattern?

Male pattern baldness or male pattern hair loss occurs when

The hairline gradually moves backward (recedes) and forms an "M" shape. Eventually the hair becomes finer, shorter, and thinner, and creates a U-shaped (or horseshoe) pattern of hair around the sides of the head.

(NLM MedlinePlus)

You'll find this term, for example, in advertisements for hair loss drugs, because it is important to distinguish between natural balding, which is usually a factor of genetics and age, and other kinds of hair loss caused by illness, malnutrition, alopecia, chemotherapy, and so forth.

It appears to me that there is no popular term for that particular stage before reaching complete baldness (see: Male Pattern Baldness). Like jxh said in a comment:

The patterns are typically numbered. E.g., Type IV or Type V, depending on who is writing the chart. The charts are typically laid out from when balding starts to when balding is near complete.

Meanwhile the internet users may call that stage as "M-shape" or "U-shape". But probably more common is "horseshoe hairline". For example, see this one from Google Books / A.D.A.M. Illustrated Family Health Guide:

The word is Semi-bald.

Male pattern baldness is when the hair-line heads north and never looks back. In this case, according to the genes of the Mother's Father, the hair-line finds a comfortable place just over the horizon. The hair will remain perfectly healthy and strong at that latitude but no further up, meaning they are no longer going bald but remain Semi-bald.

Despite the fortunate casting decision this is not a Friar Tuck hair style. The good friar shaved his head that way as all good friars do.