The term 'Alphabet Set' refers to the collection of letters used in a particular language or writing system. In the English language, the alphabet set consists of 26 letters, from A to Z. In the crossword solutions given, ALEPH is the first letter of the Hebrew alphabet, OMEGA is the last letter of the Greek alphabet, and AEIOU is a mnemonic for the vowels in the English alphabet. Together, these three solutions represent the beginning, end, and core of the English alphabet set.