Others have mentioned "arbitrary binary data", but a concrete example of that (that I know of, not that would be particularly useful to pass around) is the WASM

Others have mentioned "arbitrary binary data", but a concrete example of that (that I know of, not that would be particularly useful to pass around) is the WASM bytecode format: it starts with '\0ASM', using the NUL byte to signify to tools reading it that it isn't text and they shouldn't attempt to display it (or anything like that). However, it is a _byte_code format, and as such, it would be represented with a `char*` pointer in C. Yet, any APIs that use NUL terminated [byte]strings would stop at the very first byte, and not keep any more data beyond than that.