I tried to look for some examples; here are some from the "ShareLaTeX knowledge base." Often there are index numbers in bibliographies like this; in that case, you could say it is "in numeric order." (the term is used this way here: Biblatex bibliography styles, and here: Tips on Writing a Thesis in LaTeX) In fact, since you did not use any kind of in-line citations connecting your definitions to the previous occurrences of the word, it took me a minute or two to realize what you were doing in your question.
The default behavior listed on this page for the "none" sorting option describes this by saying "entries are processed in citation order."
That term is also used in this question: Sort thebibliography by citation order. I don't know if it's used outside of the TeX community.
As others have mentioned, it's common to use a phrase to describe this, even when in explicit contrast with "alphabetic" (Example: "how could Mellel know if the order should be alphabetic or by order of occurrence?" found on a forum about Mellel) and an extra word or two seems in my opinion a small price to pay for increased clarity.
Example of how your question could be written if the definitions were listed in numerical order:
Is there a single word to describe when something is sorted1 in "order
Bibliographies3 are often sorted like this. Names of actors/actresses
in a movie sometimes are, too.
This is in contrast to how an index is usually sorted [ie
As an example, I might say:
The definitions below are given in numerical order.
sorted: organized, arranged
appearance: the act of becoming visible
bibliography: a list of books referred to in a scholarly work
alphabetically: ordering where strings are placed in order based on
the position of characters in the conventional ordering of an alphabet