Are delimiters are used to identify a word in a regular expression. Let's create a file:

zarrelli:~$ echo "barnaby went to the bar to see the barnum musical" > text.file 

Now, we will grep with the word delimiter set to bar with the -o option, which will output only the fragment that matched and not all the lines containing it:

grep -o '<bar>' text.file 
bar

This is correct. There is only one single word called bar; the others are composite words, and we can double check this:

zarrelli:~$ grep -o bar text.file 
bar
bar
bar

If we do not look for the word named bar, but only for the matches of a three character string bar, we see that we can match it three times in the file.