A letter series is a logical grouping of letters from the English alphabet in a predetermined sequence. A sequence of letters, groupings of letters, or combinations of letters and numbers are provided in this. Each group or single piece is referred to as a word. These words can be used to communicate with others by typing on a keyboard or speaking into a microphone. There are four basic type of word lists that can be used with CAPTCHAs: alphabetic lists, phonetic lists, semantic lists and visual lists. An alphabetic list is made up of words that start with the same letter. For example, "Hello" would be the first word in an alphabetic list because it starts with the letter H. Words that end in "-y" would also be part of this list. Alphabetic lists are easy to create using Microsoft Word's Find and Replace feature. Simply select the "Alphabetical" option under Find What then click Replace All. The first word in the list will be replaced with all other words starting with the same letter. A phonetic list is made up of words that sound like each other when spoken. For example, "ball" and "slam" would be two words in a phonetic list because they both begin with the sound /b/. A semantic list is made up of words that have similar meanings.