What is the purpose of "Arrays #' that shows up below the level?

The levels in the game are divided into sections with different themes, and then each section is divided into groups with a set background picture, most of these groups contain 16 levels each. Each group has a name so your current progress puts you on the 6th level of group 'Ray'.

You can see all the sections and your completed puzzles in the groups by tapping the 3 dots button at the top of the main screen.