Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...b5/6. Bb3

=Ruy Lopez=

Ruy Lopez Arkhangelsk/Møller Variations
The move ...b5 is seen at some point in most variations of the main line Ruy Lopez, so Black has a few transpositional possibilities here: 6...d6 or 6...Be7 will probably end up in the standard Closed Variation (5...Be7 6. Re1 b5) and 6...Nxe4 almost certainly leads back to the Open Variation.

Basically, replacing ...Be7 with ...b5 means that Black has retained the option of setting up bishops at b7 and c5. The two independent moves, therefore, are the Arkhangelsk 6...Bb7 and the Møller 6...Bc5. They may transpose into each other.

It's always to Black's advantage to have something to play against the Lopez other than the old main lines, which is why these two sound, aggressive variations, along with 5...Bc5, have experienced a major revival of late.