Serialization, the process by which run-time objects are saved from memory to a persistent storage (typically disk) or sent across the network, necessitate the objects to be encoded in some efficient, preferably machine-independent, encoding.
One could consider XML or JSON, which are both viable options whenever simplicity or human-readability is required, or if every serialized object has a natural text-only representation. JSON, for example, provides only for a limited number of basic data types: number, string, bool, arrays and objects. What if you have a binary object? The standard approach with text encodings is to use Base64, but this results in an 33% data expansion, since every 3 source bytes become 4 encoded bytes. Base64 uses a-z, A-z, 0-9, +, /, and = as encoding symbols, entirely avoiding comas (,), quotes (both single and double), braces, parentheses, newlines, or other symbols likely to interfere with the host encoding, whether XML, JSON, or CSV.
What if you do not want (or cannot afford) the bloatification of your data incurred by XML or JSON, and are not using a language with built-in binary serialization? Evidently, you will roll up your own binary encoding for your data. But to do so, one has to provide not only the serialization mechanisms for the basic data types (including, one would guess, the infamous “binary blob”) but also a higher-level syntax of serialization that provides for structure and—especially—error resilience.