Soft head
(This is a stub)
Soft head (软头 {- 頭} ruǎntóu) and hard head (硬头 { - 頭 } yìngtóu) are Chinese Go terms. These terms apply to the target of a hane - like one single stone, or two or three stones in a line, where the other player can hane.
Call this target a "head" (头). Say the head is black. Given the follow-up where White hanes and Black counter-hanes, if these moves give White a useful atari or cut, then the head is called a soft head. Otherwise it's called a hard head.
The idea is simpler than it sounds. It may be useful for kyu-level players. There is a Chinese-language article which gives examples. Examples 1 and 4 are hard heads; 2, 3 and 5 are soft heads. Examples 6 - 10 illustrate how it is (generally) better to hane a soft head rather than a hard head; and how it's (generally) better to strengthen (via a solid extension/ 长 cháng / nobi) a soft head rather than a hard head.