LLL are three letter domain names, for example xyz.com. In total there are 17,576 LLL domains names. This is calculated based on the number of letters in the alphabet (26). 26x26x26=17,576 combinations.
Another example is NNN or 123.com. This refers to numbers and have fewer combinations of only 1,000 calculated from 10x10x10=1,000
Another example is NNN or 123.com. This refers to numbers and have fewer combinations of only 1,000 calculated from 10x10x10=1,000