They are both algorithm books and the initials are the last names of the authors.
AHU is "The Design and Analysis of Computer Algorithms" by Aho, Hopcroft and Ullman.
CLR is "Introduction to Algorithms" by Cormen, Leiserson and Rivest
AHU is "The Design and Analysis of Computer Algorithms" by Aho, Hopcroft and Ullman.
CLR is "Introduction to Algorithms" by Cormen, Leiserson and Rivest