Tell my your gamerscore and i will tell your future
This is a meta-goal outside that have not further effect on the future gameplay. Meeting the conditions the achievement is unlocked and it is possible for others to see how cool you are.
Each game have 1000 gamerscore points and each achievements is worth a number of points.
On PSN they are called Trophies. There are bronze, silver and gold depending on the difficulty of the accomplishment. When all is unlcoked by the player he gets a final platinum trophy.
Game Center (iOS)
Google Play Games (Android)