Score

Score is a mechanic in every game to show the player the amount of points they have achieved, as well as encouraging them to make goals for themselves to achieve higher ones the next time they play. In GH:SE, the score counter is simply a green rectangle with a black outline. The score increases every time the player hits a note or holds a sustain, and it never goes down unless the player fails or completes the song, in which case the score will be set to 0. At the end of each song, except for their own custom songs, the players can see the score they have achieved on the stats screen.

Highest score ever achieved with no cheats
The highest score ever achieved in GH:SE has to be in the hundred-thousands, but 1,000,000 or higher is only achievable on two songs, them being Uber Song and Uber Song 2. So not only is getting to one million physically challenging, but so far, it's been proved impossible, unless someone manages to FC the songs, which is impossible by all standards.

Prior to V9, 1,000,000 points was only possible on Uber Song 2. It is impossible to achieve this on Uber Song, as the closest score was 992k. Lawrence has personally tried a lot of times to reach higher than that, and it has never worked. Even when he activated Star Power in different locations to see if he could it, the result was the same.

But now, it is possible to not only get 1,000,000 on Uber Song, but 2,000,000 as well and if you want an extra challenge, 3,000,000, which can only be obtained with a bot and the right circumstances of Star Power activating.

Trivia

 * In the original Guitar Hero III, it has been proved possible that 1,000,000 points is possible on Through the Fire and Flames, but so far, there was no proof of it ever shown.
 * Despite the Note Streak having a limit of 10 quadrillion, the Score limit is way higher, being at 2^59 (2 to the power of 59), or 576,460,752,303,423,488 (five hundred and seventy-six quadrillion, four hundred and sixty trillion, seven hundred and fifty-two billion, three hundred and three million, four hundred and twenty-three thousand, four hundred and eighty-eight). The scary part is, even THAT is impossible to get to, as it would take roughly 1,125,899,906,843 seconds, or just over 35,702 years to accomplish (assuming you the FPS remains at 32).