Wordpress browser caching

By specifying a longer caching period for your web page components (HTML, images, Javascripts, CSS documents, etc.), web browsers will cache these elements locally so that they don’t need to be downloaded from the server each time the page is accessed.

You may leverage browser cache by adding the following code to the .htaccess

<IfModule mod_headers.c>
# YEAR
<FilesMatch ".(ico|gif|jpg|jpeg|png|flv|pdf)$">
 Header set Cache-Control "max-age=29030400"
</FilesMatch>
# WEEK
<FilesMatch ".(js|css|swf)$">
 Header set Cache-Control "max-age=604800"
</FilesMatch>
# 24 HOURS
<FilesMatch ".(html|htm|txt|php)$">
 Header set Cache-Control "max-age=86400"
</FilesMatch>
</IfModule>

source: http://www.bluehost.com/blog/educational/websites/the-ultimate-guide-to-supercharging-your-wordpress-blog-2097/