The word 'navigation'

the word navigation where ?

you can enable the locale module and create a site specific language that changes all uses or navigation to something else but this may not be the best method depending on where exactly you are trying to change this specific word.

to use the locale module to accomplish this and create a site specific language these handbooks pages will proove useful http://drupal.org/handbook/modules/locale

The built-in 'navigation' menu label doesn't seem to be editable from administer >> menus but you can control its placement and visibility via administer >> blocks. You can however create new names for other default menu labels like 'news aggregator' by disabling it in administer >> menus and then creating a new menu category under which you can add your feeds as menu items.

Check this out at http://drupal.org/node/97442#comment-190397

In addition to the above methods, you can do the following two methods if you really do not want to install locale module(I did not want to because the more modules you use, the slower it can be on some webhosts, lesser is better in some places.)

Before making any changes, make a backup of the file here so you can go back to your default stuff if anything goes wrong.

First -> Find and open the 'drupalinstallationdirectory'/includes/menu.inc file. Search for

'title' => t('Navigation')

It can be around the 1027th line in the file. All you have to do is to change the 'Navigation' to 'anything' you want so it looks like this.
'title' => t('anything')
It will then appear with that 'anything' even when you are in the admin/menus path or anywhere else in the site.

Second -> I had a different need, wanted one menu title for logged in users and another for anonymous.
I added the following code directly in there just below the global $user; around the 1018 line and above the $_menu = array(); part of the file.

// Custom code to make the login menu say customized username after logging in, else show nothing

$navigation = 0; // defining a variable in php
if (!$user->uid) {
// Change the following line's text to whatever you want.
$navigation = 'Hello';
}
elseif ($user->uid) {
// The following line will display a custom line(welcome- in my case) plus the username of the person.
$navigation = 'Welcome ' . check_plain($user->name);
}

Then I changed the 'title' => t('Navigation') as stated above to

'title' => t($navigation)

Note that this time, when I use a variable=$navigation, there are no quotes inside the brackets. If you include the quotes you will end up seeing $navigation as the menu heading rather than what you specify.

Hope this helps, it really helps if you want to save up on db access with the number of modules used.

http://www.dilipfrancis.com/