The Grapple Beam was one of Samus Aran's many weapons. It first appeared in Super Metroid though it was called the Grappling Beam at the time. The Grapple Beam was used to latch onto certain surfaces, giving Samus some new maneuvers such as swinging from the ceiling. Notably, the Grapple Beam can be used to kill Draygon quickly by grabbing one of the electrified surfaces while in the grip of the boss. It can damage enemies directly, though due to its range and firing speed, it is impractical for this function, although it works very well against Mochtroids. It can also be used to open Blue Doors.
It has also appeared in Metroid Prime, where the Grapple Beam was primarily used to get across long distances. Samus was able to shoot while swinging on it in Metroid Prime 2: Echoes, while Metroid Prime 3: Corruption uses it to pull barriers from doors and shields from Pirates (Grapple Lasso), and later on, siphon and feed energy to and from certain devices (Grapple Voltage), using the Wii Remote and Nunchuk.
In Metroid Prime 3: Corruption, there are four Grapple Beam-related powerups:
Somewhat notably, in all of the 3D Metroid games, the grapple beam was no longer fired from the Arm Cannon. Instead, a second firing piece, or a glove of sorts (in Prime 3) was used (both on her left hand). This is likely to make it more real-looking, make more use of Samus's free hand, and/or to free up the Arm Cannon for shooting in the sequels.
The Grapple Swing is the game's name for the traditional Grapple Beam power-up, except in Corruption, where it is a separate power up (due to the new upgradable "glove") that allows Samus to swing from Grapple Points.
Samus's gunship also gains a Grapple Beam towing cable power-up, that gives Samus the ability to transport various large objects by having her Gunship fly in and grapple them via the ship-mounted Grapple Beam.