This is a word transliterated and adapted from Greek παρεκβολή (parekbolḗ), from πᾰρά (para-, "near", but here meaning "placed together") and ἐκβολή (ekbolḗ, "throwing out" but here meaning "something tossed off"), which together can be a "compilation of a set of critical remarks":
I. digression, lamb.Bab.8.
II. compilation of a set of critical remarks, as those of Eust. on
Homer, Pindar, and Dionysius Periegeta, cf. eund. ad D.P.426;
παρεκβολαὶ διαφόρων γραμματικῶν, title of Sch.D.T. in
— Liddell, Scott, Jones
As the word sive ("or", "or also", "also called") indicates as well, the plural parecbolae is used here as a synonym of excerpta. The author names his work parecbolae, to which he adds excerpta as an explanation or translation for those who might not know the word parecbola.
It might be a fairly late adaptation, for I couldn't find any classical Latin sources. Parécbole is in a Portuguese dictionary: https://www.dicio.com.br/parecbole/ It's also used in a few other languages, amongst which English, but very rarely (Google search results). There is mention of a Parecbole by Eustathius of Thessalonica (a major Byzantine scholar), then the book from the question, and also a gloss describing the meaning of the word in general, through referring to the work by Eustathius. References to parecbolae on/from Aristotle by Theodorus Metochites (another major Byzantine scholar) can be found as well. Then there are a few more results (in addition, no doubt, to other uses of the word outside Google's limited reach).