Highlight all occurrence of a selected word?

In Normal mode:

:set hlsearch

Then search for a pattern with the command / in Normal mode, or <Ctrl>o followed by / in Insert mode. * in Normal mode will search for the next occurrence of the word under the cursor. The hlsearch option will highlight all of them if set. # will search for the previous occurrence of the word.

To remove the highlight of the previous search:

:nohlsearch

You might wish to map :nohlsearch<CR> to some convenient key.

The * key will highlight all occurrences of the word that is under the cursor.

I know than it's a really old question, but if someone is interested in this feature, can check this code http://vim.wikia.com/wiki/Auto_highlight_current_word_when_idle

" Highlight all instances of word under cursor, when idle.
" Useful when studying strange source code.
" Type z/ to toggle highlighting on/off.
nnoremap z/ :if AutoHighlightToggle()<Bar>set hls<Bar>endif<CR>
function! AutoHighlightToggle()
   let @/ = ''
   if exists('#auto_highlight')
     au! auto_highlight
     augroup! auto_highlight
     setl updatetime=4000
     echo 'Highlight current word: off'
     return 0
  else
    augroup auto_highlight
    au!
    au CursorHold * let @/ = '\V\<'.escape(expand('<cword>'), '\').'\>'
    augroup end
    setl updatetime=500
    echo 'Highlight current word: ON'
  return 1
 endif
endfunction