The "[Masoretic Text](https://en.wikipedia.org/wiki/Masoretic_Text)" of the Hebrew Bible includes as part of its "mark up" a set of marginal readings known to the Torah scholars who transmitted the text in that form. These variants are known as ["*ketiv* and *qere*" readings](http://www.reltech.org/TC/v08/Graves2003.html):

- *ketiv* = what is "written" (*ketiv*), and appears in the text itself;
- *qere'* = what is "read" (*qere*), and this is the marginal reading.

The *qere* "Perpetuum" are those readings where the Masoretes (these "Torah scholars") have a *ketiv*, but *without* an accompanying marginal *qere*. The parade example is the 3rd person singular independent pronoun in the Pentateuch: very many times you get h-w-ʾ (*hûʾ*, masculine) where you expect h-y-ʾ (*hîʾ*, feminine). In this case the Masoretic text has the *vowel* marking of the latter, with the consonants of the former, leading to the anomalous: הִוא. So in *every* case where this appears the *ketiv* is seen, but the (unmarked) *qere* is pronounced (*hîʾ*) - in "perpetuity", as it were. The first time this occurs is (I think) in Genesis 3:12, the last time in Deut 30:13, altogether 128 occurrences.

See Gesenius-Kautzsch-Cowley, *[Gesenius' Hebrew Grammar ](https://openlibrary.org/books/OL7085598M/Gesenius%27_Hebrew_grammar)* (2nd edn; Clarendon Press, 1910), at [§ 17c, p. 66](https://archive.org/stream/geseniushebrewgr00geseuoft#page/66/mode/1up) for technical explanation.