Power-ups or upgrades are collectible items that Samus Aran uses in every Metroid game to gain new abilities. In the series, there are many different kinds of power-ups, which include more powerful Beams, Morph Ball functions, grapple and movement systems. They will usually give Samus an ability that she needs to reach and explore a new area.
Power-ups in most Metroid games are pieces of Chozo technology used to expand the Power Suit, but in the series Samus also uses power-ups of Luminoth, Alimbic and Galactic Federation origin. The latter, in Metroid Fusion, gives Samus Power-ups through Data Rooms, where she downloads the upgrade to her Power Suit. Expansions for certain power-ups can be collected to increase ammunition or energy capacity.
Not all power-ups may be needed to clear the game, and some required ones can be skipped through Sequence Breaking. Items such as the Spring Ball in Super Metroid make exploration easier, but are otherwise optional.
In most of the games, a power-up's appearance is a symbol for what it does; for example, the Morph Ball Bomb power-up is a case with a bomb in it. The Screw Attack power-up icon (usually a red or purplish-black ball with a small yellow lightning strike on it) is used in several Metroid game logos.
Many power-ups can be found in the hands of a Chozo Statue; if this is the case, then the power-up will often be concealed in a protective casing referred to as an Item Sphere. To break the sphere, all Samus has to do is shoot it with any beam. Some power-ups will float in mid-air until Samus touches it (this is common if the power-up is gained from a boss, an example of this is the Charge Beam in Metroid: Zero Mission), some are placed on various pedestals in rooms, and some of them are hidden in various places and sit on nothing in particular.
In Metroid: Other M, all power-ups except the Diffusion Beam, Seeker Missiles, Missile Expansions, Energy Tanks, E-Recovery Tanks and Accel Charges are in the possession of Samus, but out of respect for Adam Malkovich she refrains from using them, though he gradually allows her to use them and sometimes she activates them without his explicit permission. In Metroid Fusion, some power-ups are received as data and do not have a physical form. Metroid Fusion also has power-ups in the form of an enemy, the Core-X, which must be absorbed to receive power-ups. To help Samus find the better-hidden items in the Metroid Prime games, all power-ups will give off a faint humming noise to advertise their presence.
"Occasionally you'll come across items that enhance Samus's physical abilities. All of these can be activated and deactivated on the status screen."
Metroid Prime manual
"As Samus delves deeper into the Space Pirates' operation, she'll find power-ups that improve both her arsenal and her suit. Every power-up she finds will help her access something new in vast regions of Tallon IV, so remember areas where she can't progress and return once she's gained new abilities. Pay special attention to the colors of closed doors, as they should help you determine what weapons you need to use to open them."