The Index Type dropdown list defines the type of the table index. PostgreSQL provides the index methods B-tree, R-tree, hash, and GiST. The B-tree index method is an implementation of Lehman-Yao high-concurrency B-trees. The R-tree index method implements standard R-trees using Guttman's quadratic split algorithm. The hash index method is an implementation of Litwin's linear hashing. Users can also define their own index methods, but that is fairly complicated.
Unique
Makes index unique, causes the system to check for duplicate values in the table when the index is created (if data already exist) and each time data is added.
Clustered
CLUSTER instructs PostgreSQL to cluster the table specified by tablename based on the
index specified by indexname. The index must already have been defined on tablename.
When a table is clustered, PostgreSQL remembers on which index it was clustered. The form CLUSTER tablename reclusters the table on the same index that it was clustered before.