Ladder

Ladders are found on the Biologic Space Laboratories research station. In Metroid Fusion, ladders are always bars protruding from a surface. They can be climbed as well as jumped and fired from on both walls and ceilings.

LADDERS: "Samus can grab on to ladders by facing and jumping toward them.
To let go of a ladder, use the +Control Pad to choose a direction and then press the A Button. Samus will always do a Spin Jump off ladders.
To shoot while on ladders, use the +Control Pad to aim and press the B Button."

Exactly how Samus climbs the ladder with one hand and the Arm Cannon is unknown. In Metroid Fusion, whenever Samus's sprite would display the Arm Cannon holding on to a ladder, she will always quickly adjust herself so that she is hanging on to a ladder with her left hand. This is easily seen on horizontal ladders, where the sprite will rapidly advance frames to apply the proper hanging position.
Samus is also able to climb and slide down ladders in Super Smash Bros. Brawl in both her Zero Suit and Varia Suit, but cannot fire from them.
Ladders also appear in Metroid: Other M (such as in the slender walkway), however, they are part of the scenery and cannot be used by Samus.
Blue magnetic strips in Metroid Dread play a similar role to ladders, although they require the Spider Magnet to use.