Glossary
Enemy spotted
In one line: The red marker on the minimap: an enemy a teammate (or an ability) can see right now.
What it means
When a teammate sees an enemy, that enemy shows up on your minimap as a red marker, even if nobody says anything. Many recon abilities do the same. Once they are no longer seen, the minimap briefly keeps their last known position.
It is free information that many players miss because they never look at the minimap. One caveat: the marker shows where the enemy was at that moment, not where they will be five seconds later. Read it together with sound and time.
An example
You are holding B and three red markers pop up in mid, spotted by your teammate there. Nobody said a word, but you now know that at most two of them can be coming to B for now.