Alexandrian text-type refers to the earliest New Testament manuscripts, which were typically preserved in the dry climate of Alexandria, Egypt. The earliest examples date back to the 2nd century, such as "P66" and "P75" (names given to early manuscripts). The oldest virtually complete manuscripts, which are also of this type, are the Codex Sinaiticus (held in the British Museum) and the Codex Vaticanus (as its name suggests, held in the Vatican library).
It is these texts which adherents of the King James Only movement consider "corrupt"; since many of these texts were incorporated into Greek texts comprising most newer translations; by extension, adherents refuse to accept the translations as "God's pure words".