This is a
Counter-Strike: Global Offensive (Csgo) term.
In Csgo there is a utility grenade that gives a
competitive advantage when used correctly, called a smoke grenade, or smoke for short. This term revolves around the usage of the smoke grenade.
An "one way" is refering to a cleverly placed smoke grenade that allows only one direction of vision. In other words: "I see you, but
you can't see me."
This happens commonly in Csgo because the game is extremely competitive and any advantage will cause a victory.
The term became popular because it's a quick way to alert your team of the threat, because an one way smoke will cause massive losses to the enemy.