Type coercion = Allow types to be converted to other types automatically to perform some operations like comparison.

Type corrosion = some non-standard condescending term to say that dynamic typing has no proper rigid types?

No it's not, they're completely different concepts. In C/C++ lingo Dynamic typing is having every variable be a void * whereas type coercion is implementing conversion functions for your types to allow casting between types, e.g. having a temperature class that can be casted to a double (or from it).

This is a function with dynamic typing and no type coercion in C/C++:

int foo(void* param) {
  Temperature* t = (Temperature*) param;
   return t->intValue() + 10;
}

This is the same function with type coercion and no dynamic typing in C/C++:

int foo(Temperature& t) {
  return t + 10;
}