Serialization is the process of writing arbitrary data out into a blob of some sort (binary, text, whatever) that can be read in later and processed back into the original data, possibly not by the same system. This should be considered to include even the degenerate case of just writing the content of an expanse of RAM out, as that still raises issues related to serialization.
"JSON Serialization" and "Java Serialization" are two different things that can accomplish that goal. It sounds to me from your question that you think they have some fundamental difference, because your second paragraph implies you believe there is some sort of fundamental difference between Java serialization and JSON serialization, but there isn't. There is a whole host of non-fundamental differences that you always have to consider with a serialization format (speed, what can be represented, circular data structure handling, whether untrusted data can be used), but there's not a fundamental difference.
"JSON Serialization" and "Java Serialization" are two different things that can accomplish that goal. It sounds to me from your question that you think they have some fundamental difference, because your second paragraph implies you believe there is some sort of fundamental difference between Java serialization and JSON serialization, but there isn't. There is a whole host of non-fundamental differences that you always have to consider with a serialization format (speed, what can be represented, circular data structure handling, whether untrusted data can be used), but there's not a fundamental difference.