Bombs are a "weapon" that are primarily used while your in Morph Ball mode and their main function usually is to bomb through breakable blocks, rather then hurt enemies since there not a particularly powerful offensive weapon.
Bombs are featured in most Metroid games and are usually the second item you acquire, after Morph ball.
A much more powerful and effective bomb based weapon are Power Bombs, which have a very wide blast radius that destroys\damages all blocks and enemies in their vicinity.
Bombs are often used to speed break certain areas which is known as "bomb jumping". A skilled enough user can bomb jump infinitely.
Bombs is the second upgrade that appears in the game and is found directly after Morph ball.
They are found in Brinstar and are a very important item in the game as many secrets and ways to progress are usually found in bombable walls and floors.
 Metroid 2: Return of Samus
Bombs return in this game and function more or less the exact same way they did in the original game.
They appear early on in a Chozo looking temple.
 Super Metroid
Bombs make a return and work like they do in the previous games. Unlike the previous games however one must defeat a mini boss in the form of a living Chozo statue, in order to get them.
They are located in Crateria and you require the Morph ball in order to get them as they are located down a hole only accessible with Morph ball.
As mentioned they are guarded by a living Chozo statue, or more specifically, a Torizo.
Once you grab the bombs, the metal will peel off the statue revealing the Torizo and it will start to attack you
It's attacks consist of throwing bombs and energy waves.
A few shots from missiles or the power beam will destroy it and you will be free to progress into Brinstar.
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