Serialization is the movement of structured data across a storage / transmission medium so that the structure can be supported. Coding is broader, for example, how converted data is converted into different forms, etc. You might have thought that serialization is a subset of the coding in this example.
As for the web service, you are likely to consider serializing / deserializing certain data to create / receive requests / responses - efficiently transporting “messages”. The encoding is at a lower level, for example, how your messaging / web service / serialization mechanism works under the hood.