Blinding
A blind is any wall or pillar that you can hide behind to shoot people without being seen. You can blind people by catching them in your trail vision, then going behind a wall or pillar. They won't be able to see you, and you can shoot them without any fear of dying.
Examples of pillar blinds in game. In each example I'm able to stand behind the pillar and shoot my opponent without them seeing me, because I grabbed some trail vision before going behind the pillar.
There are blinds everywhere in the map. The best way to learn is to watch a more experienced player and see what things they hide behind. In general, a blind only works in a specific direction, so if your opponent comes from a different direction or angle then they might be able to see you.
Video walkthrough of blinds.