Sweep & Latch: The range of the door closer arm is broken into an initial 90 - 160 degree (depending on the swing range to fully open position) “sweep” range when the door moves slowly and the final 5-15 degree “latch” range when the door moves more swiftly. The latch range moves quickly at the end of the closer stroke to ensure full closure regardless of the expected friction and rubbing as the door sweep and seals engage to ensure a more or less air tight closure. The sweep and latch range speeds of the door closer can be adjusted using a screw driver or hex wrench on the screws typically marked "S" and "L" respectively.
Recoil & Delay: In addition, there are often Recoil and Delay adjustments elsewhere on the closer body. Recoil protects the door and surroundings from doors being hurled open by excessive force or getting caught in a gust of wind. The Delay adjustment can pause the door in the open position for up to a minute before closing.
Too Heavy: Some door closers have springs that can be adjusted to control how "heavy" a door is (how much force it takes to push it open against the closing force of the closer. If a closer does not have this adjustment (it is rare and expensive) the position of the closer on the door can be moved closer to or farther from the hinge to increase or decrease the lever arm advantage of the door. (Bob Cowherd 2018)