Cast is explicit. Coerce is implicit.
The examples in Python would be:
cast(2, POINTER(c_float)) #cast
1.0 + 2 #coerce
1.0 + float(2) #conversion
Cast really only comes up in the C FFI. What is typically called casting in C or Java is referred to as conversion in python, though it often gets referred to as casting because of its similarities to those other languages. In pretty much every language that I have experience with (including python) Coercion is implicit type changing.