Quick and dirty "goto definition" that looks up for the last selected (in visual mode) string.

my_GotoDefinition.vim

function! GotoDefinition()
  let selectedStuff = s:get_visual_selection()
  if strlen(selectedStuff)>0
    exe 'vimgrep /' . selectedStuff . '/ **/*'
	  exe 'copen'
  elseif
	  echo 'Nothing selected. Aborting.'
  endif
endfunction GotoDefinition

" https://stackoverflow.com/a/6271254
function! s:get_visual_selection()
  " Why is this not a built-in Vim script function?!
  let [lnum1, col1] = getpos("'<")[1:2]
  let [lnum2, col2] = getpos("'>")[1:2]
  let lines = getline(lnum1, lnum2)
  let lines[-1] = lines[-1][: col2 - (&selection == 'inclusive' ? 1 : 2)]
  let lines[0] = lines[0][col1 - 1:]
  return join(lines, "\n")
endfunction

command! GotoDef call GotoDefinition()