'Available' means that the web server responded successfully with HTML for the page.

'Usable' means that the page was available and also met the following usability criteria: speed of 5kB/sec or greater, response time of 1 second or less, no accessibility priority 1 (A) failures, no errors, and 7 or fewer warnings.

Functional Failures (errors) - Prevent your site from working correctly. Examples include: faulty email addresses, server errors, broken links, DNS setting and bad paths on the site.
Code Failures (warnings) - Are poor operating code and are frequently violations of W3C or IETF standards. These may affect the visual display of your site or slow it down.
Response Time - is the average time taken by the server to respond to a request to access an object.
Download Speed - is the average speed at which the server transmitted data to the Sitemorse™ system during the test.