Bash allows auto-completion using the tab key:
If you type
cd ~/D on Terminal, followed by the Tab key, you ear a beep, but if you follow by a second Tab key, the Terminal display the suggestions
Desktop/ Documents/ Downloads/. If you type "e" followed by Tab, the auto completion displays
cd ~/Desktop/, that is (here) the only folder in Home folder who begins with "De".
For whatever reason it stops to work for me after a while using Terminal or Iterm2. How can I diagnose and fix this?