:global

:s (:substitute) is one of the first commands any Vim user learns. There are several similar commands that are more generic. Like :s, these commands can take a range; however, unlike :s, there is no % variant, as these commands are global by nature.
These commands can be seen as a simpler, less general-purpose alternative to macros that takes less keypresses.
Commands
:g (:global)
Instead of substituting strings matching the first part with the second, runs the (command mode) command on strings matching the first part.
:v (:vglobal) (equivalent to :g!)
Same as :g, but targets strings that do NOT match.
Use cases
Delete lines containing pattern
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g/pattern/d
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Practical usage:
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g/TODO:/d
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g/debugger/d
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g/binding.pry/d
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Optimization: g/pattern/_d puts deleted lines in the null register, which has no performance cost.
Conditional find/replace
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g/pattern/s/word/newword
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This "scopes" the substitution to matching lines (for example, to scope your substitution to comments).
Yank all matches
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g/pattern/y A
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Note that we are yanking to an uppercase register, meaning we append matches. If we did y a, each yank would overwrite the previous yank.
:norm
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g/pattern/norm ^ihello
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This applies the normal mode instruction (here, "go to start and insert hello") to matching lines.
Practical usage:
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g/debugger/norm gcc
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g/pattern/norm @q
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:exe
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g/pattern/exec "norm!" "A\r"
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When using :norm, you might notice that you can't insert linebreaks --  and <CR> is literally printed as the strings "\r" and "". :exec(ute) lets us actually pass in commands as strings to be executed, like eval().
This is a somewhat meta pattern that follows the last example. It executes the two separate commands "norm!" and "A\r" to the pattern. Before execution, the second is evaluated to "append carriage return."