"Key" seems to mean quite a few different things. Good catch, it would involve a lot of manual retagging though doesn't matter anymore though :P
Let's see:
Mechanical keyKeyboard keys
The stuff aBoth the physical ones on the keyboard is composed ofand the conceptual ones like hotkeys, key-combos, and keystrokes that perform functions. Mostly in combination with keyboard, keyboard-shortcut or, keyboard-layout, hotkeys.
Registry Keykey
The ones used in Windows Registry. Mostly in combination with registry.
SSH KeyCryptographic keys
AnEncryption keys as in PGP. Mostly in combination with php or cryptography.
SSH keykeys generated by ssh-keygen tool. Mostly in combination with ssh.
Database keys
Keys as used in databases. Mostly in combination with odbc, access, etc.
Serial numbers
CD keys, product keys, serial numbers, et. la. Mostly in combination with registration or activation.
