Tag is what goes after the struct keyword to allow referring to the struct type. Structs don’t have to have a tag. Name is what field are called. Adapting Obin’s example:

struct foo { int baz; };
struct bar { struct foo qux; };
struct bar data;
data.qux.baz = 0;

foo and bar are tags for struct foo and struct bar types respectively; baz and qux are field names; and data is a variable name.