DEFLATE is a lossless data compression algorithm similar to gzip, but it works in Apache 2. 
In the past, mod_gzip was a recommended tool. But DreamHost uses Apache 2 and mod_deflate, which calls gzip on the back end automatically.

<ifmodule mod_deflate.c>
  # Compress HTML, CSS, JavaScript, Text, XML and fonts
  AddOutputFilterByType DEFLATE image/svg+xml
  AddOutputFilterByType DEFLATE application/javascript
  AddOutputFilterByType DEFLATE application/rss+xml
  AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
  AddOutputFilterByType DEFLATE application/x-font
  AddOutputFilterByType DEFLATE application/x-font-opentype
  AddOutputFilterByType DEFLATE application/x-font-otf
  AddOutputFilterByType DEFLATE application/x-font-truetype
  AddOutputFilterByType DEFLATE application/x-font-ttf
  AddOutputFilterByType DEFLATE application/x-javascript
  AddOutputFilterByType DEFLATE application/xhtml+xml
  AddOutputFilterByType DEFLATE application/xml
  AddOutputFilterByType DEFLATE font/opentype
  AddOutputFilterByType DEFLATE font/otf
  AddOutputFilterByType DEFLATE font/ttf
  AddOutputFilterByType DEFLATE image/x-icon
  AddOutputFilterByType DEFLATE text/css
  AddOutputFilterByType DEFLATE text/html
  AddOutputFilterByType DEFLATE text/javascript
  AddOutputFilterByType DEFLATE text/plain
  AddOutputFilterByType DEFLATE text/xml
  # Remove browser bugs (only needed for really old browsers)
  BrowserMatch ^Mozilla/4 gzip-only-text/html
  BrowserMatch ^Mozilla/4\.0[678] no-gzip
  BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
  Header append Vary User-Agent
</ifmodule>





Using mod_expires, you can tell visiting browsers to hold on to certain files longer (likes images, which are rarely changed):

# BEGIN Expire headers  
<IfModule mod_expires.c>  
  # Turn on the module.
  ExpiresActive on
  # Set the default expiry times.
  ExpiresDefault "access plus 2 days"
  ExpiresByType image/jpg "access plus 1 month"
  ExpiresByType image/svg+xml "access 1 month"
  ExpiresByType image/gif "access plus 1 month"
  ExpiresByType image/jpeg "access plus 1 month"
  ExpiresByType image/png "access plus 1 month"
  ExpiresByType text/css "access plus 1 month"
  ExpiresByType text/javascript "access plus 1 month"
  ExpiresByType application/javascript "access plus 1 month"
  ExpiresByType application/x-shockwave-flash "access plus 1 month"
  ExpiresByType image/ico "access plus 1 month"
  ExpiresByType image/x-icon "access plus 1 month"
  ExpiresByType text/html "access plus 600 seconds"
</IfModule>  
# END Expire headers