what can replace hook I am a newbie into Drupal.

what else other than module name can replace 'hook' from any hook function in Drupal? 
For ex. 
"myModule" replaces hook in hook_form_alter and defined as 'myModule_form_alter'
Any alter hook and preprocess hooks that is defined inside a module can also be defined inside the theme as well. So if you are using Bartik theme you can open the Bartik's template.php file and use

function bartik_form_alter(){}




UPDATE

Checking the Is it possible to define hook functions in template.php instead of the module? can also be helpful.