Thanks for requesting this page! Do you want to have a go yourself, @ahmetb?
Pages are best created by people who understand the command they are about.
If you do, take a quick read of CONTRIBUTING.md, which guides you through the process of creating a new page here. Then, just simply send a pull request to this repository - and if you need any assistance, just ask :-)
I wish I understood this command well enough to write about it but I currently do not.
I can neither find where in man nor in the web.
Did you mean the whereis command? If so, I did submit a pull request for it: #1708.
Try it on your bash. There might not be a manpage for it, but it鈥檚 a command.

Hmm it works in my macOS + bash/zsh, I use it all the time. man where brings up BSD General Commands Manual.
$ where git
git: aliased to hub
/Users/ahmetb/.homebrew/bin/git
/usr/bin/git
Looks like this command is simillar to whereis in linux:
[av@av-pc ~]$ whereis git
git: /usr/bin/git /usr/share/man/man1/git.1.gz
But I think there is some difference, so we need two separate _tldr_'s:
osx/where.md.linux/whereis.md (#1708).Yes, we need 2 separate pages in that case.
where is a csh built in, but it seems zsh has it as well
man 1 csh shows tcsh manual, which contains following
where command (+)
Reports all known instances of command, including aliases, builtins and
executables in path.
Note that where is not available in bash
Previous commands seem to suggest this is an osx thing, I believe that is incorrect.
Also notice the difference between where and whereis and which

(platform: osx)
@agnivade Please read.
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Yes, we need 2 separate pages in that case.