If you want iTerm2 to behave like the other Mac OSX applications, so that alt + left moves the previous word, alt + right moves to the next word and alt + backspace deletes the whole word, add these keyboard shortcuts from iTerm > Preferences > Profiles > Keys:
- Alt + left: Send Escape Sequence, Esc + b
- Alt + right: Send Escape Sequence, Esc + f
- Alt + backspace: Send Hex Code, 0x17