According to this post an indeterminate value is:
3.17.2
1 indeterminate value
either an unspecified value or a trap representation
Accordi
When the standard introduces a term like indeterminate, it is a normative term: the standard's definition applies, and not a dictionary definition. This means that an indeterminate value is nothing more or less than an unspecified value, or a trap representation. Ordinary English meanings of indeterminate are not applicable.
Even terms that are not defined in the standard may be normative, via the inclusion of normative references. For instance section 2 of the C99 standard normatively includes a document called ISO/IEC 2382−1:1993, Information technology — Vocabulary — Part 1: Fundamental terms..
This means that if a term is used in the standard, and is not defined in the text (not introduced in italics and expained, and not given in the terms section) it might nevertheless be a word from the above vocabulary document; in that case, the definition from that standard applies.