$ man grep | grep -A6 -w "\-w"
       -w, --word-regexp
              Select only those lines containing matches that form whole words.  The test is
              that  the  matching  substring must either be at the beginning of the line, or
              preceded by a non-word constituent character.  Similarly, it must be either at
              the  end  of  the line or followed by a non-word constituent character.  Word-
              constituent characters are letters, digits, and the underscore.   This  option
              has no effect if -x is also specified.

$ cat > test.txt
www-app-kuku
www-app-kukuzzz
www-app-kukubbb
$ grep -w "www-app-kuku" test.txt 
www-app-kuku