This entry is virtually identical with those of Aelius Dionysius,  ̓Αττικὰ ὀνόματα epsilon79, and Photius, Lexicon epsilon2403 (cf. 2405). See also, post-Suda, Etymologicum Magnum 402.23 (Kallierges), the paroemiographer Apostolius (11.29), and Eustathius, Commentary on the Odyssey vol. 2.201 lines 43ff. The entry is primarily in reported speech, which appears in its correct context in Eustathius and elsewhere.
Passing references to 'Ephesian letters' are extant as early as the 4th. century B.C. (Anaxilas [alpha 1985] fr.18.6-7 Kassel-Austin describes someone 'carrying fine Ephesian letters in stitched leather'), and similar allusions without explanation occur in (e.g.) Menander (fr.274 Kassel-Austin: see under alpha 1139) and in Plutarch's Table-Talk (Moralia 706E). Explanation begins in the 2nd. century A.D.: besides Aelius Dionysius (above) see Pausanias the Atticist,  ̓AΤτικω̂ν ὀνομάτων συναγωγή epsilon85, and Diogenianus (4.78). Clement of Alexandria, Stromata 5.8.45.2ff., and more briefly Hesychius epsilon7401 give the six words which purportedly comprised the canonical incantation (askion kataskion lix tetrax damnameneus aisia/aision), with allegorical explanations of each; earlier, incomplete versions occur on lead tablets from the 4th. century B.C. onwards.
The meteorite that may have served as head for the famous statue of Artemis at Ephesus ("Diana of the Ephesians") was said to be inscribed with letters incomprehensible to all but chosen practitioners of spells and incantations, designed to ward off evil. Their practice of using incomprehensible magical phrases and names spread from Ephesus throughout the Greek world. Thanks to the discovery of many magical papyri we have a good collection of this abracadabra. (If the goddess of the witches, Hecate, appears to you at a dangerous place such as a triple crossroad, you might try saying to her, three times before you run away, A̓σκει κατασκει ερων ορεων ιωρ μεγα σεμνυηρ βαυι . "Aski kataski" is a recurrent invocation.) St. Paul, during a visit to Ephesus, encountered the practitioners of these "curious arts" and succeeded in having them burn many of their sacred books (Acts 19.19).
Modern discussion of the Ephesia grammata is extensive. Bernabe [below] gives and discusses secondary bibliography in full, besides giving a full dossier of the primary sources. His article is very useful even if one dissents from the specific views its author holds and argues for, such as the Orphic origin/character of the grammata (and the opinion, following Wuensch, that the adjective associated with them is lower-case -- not Ephesia but merely ephesia, 'liberating/loosening').
[1] King Croesus of Lydia (kappa 2497, kappa 2498, kappa 2499, kappa 2500) was miraculously saved from this pyre, allegedly by his use of these spells.
[2] Adler does print the transmitted numeral 'thirty' (τριάκοντα ), but it can hardly be right. Proposed emendations are τρίς ('three) and τρὶς ἄκοντα ('three involuntary').