Web.com has merged the SnapNames and NameJet inventories. So when you do a search for NameJet, SnapName domains will show up, and vice versa.
Alexa Internet Inc provides alexa rankings for websites based on the data collected from it's toolbars. Since the data is collected from a sample subset of the population that has the toolbar installed, it may not be very accurate. The various metrics are given below
Alexa Rank: This is the current rank that the domain has based on the last three months of data
Top Rank: This is the highest rank that the domain has ever reached
Rank Delta: This is the change in rank from the previous rank (from three months ago). A negative number means that the rank has increased from before.
Country Rank: If the domain is popular in a particular country then Alexa gives the ranking for the domain in that country
Back Links: The total back links to the domain based on Alexa data
Address Information: The registration address and details
Related Sites: List of sites related to the domain