Density is the term used by SQL Server to represent the selectivity of the index columns. The more selective an index is, the more useful it is in searches. Density values range from 0% to 100%. A unique index will have a Density value of 1/(#rows in table). Generally, density values of 10% or lower are highly selective indexes. Density can be difficult to interpret as the value is a function of the number of records in the table.
Avg Key length
The average length of all the index columns.
The time and date that the statistics were last updated.
The number of rows in the index.