The Roblox ID is a source of when the players or other items were created in relation to other items. The ID number can be seen at the URL on a user or item page. To calculate ID, the smaller the ID number, the longer the item or user has been on ROBLOX; the longer the ID, the shorter the item has been on ROBLOX. For example, ROBLOX's ID is 1, which means ROBLOX was the first user. This is useful for scripts, telling who stayed on ROBLOX the longest, and for other sources. ID numbers are different by types, such as places have their own ID, and user ID doesn't correspond with place ID.
In the past, the administrators attempted to replace user IDs with users' names instead, but it led to many problems.