Your net position is how far ahead or behind you are overall: everything won minus everything staked. Since 31 October 2021, GB-licensed online slots must display it, along with how long you have been playing.
The rule exists because a game's balance and win animations do not tell you clearly how you are doing. A string of small wins can feel positive while you are steadily losing, especially when many of them are losses disguised as wins. Net position makes the true figure visible.
Watching it alongside the time played is one of the simplest ways to stick to a plan for a session. See game design rules.