AJAX is not different from Javascript.
Like , a child can't be differentiated by a mother.
AJAX is a acronym for 'Asynchronous Javascript And XML'.

AJAX is a new approach towards page reloading.

If you want a specific book , you will purchase that book
and not the whole book store.

Similarly if you want a small part of the data in a web page 
, you will not go for whole page reload, you woould prefer
to get the data you want.