Someone pls, what it means this in the sql query "INDEX = PK_DPAGODOCUMENTO"

everyone ... im stuck with this query, that was lefted by another programmer, i search and search by really i had no clue, if someone can give me a guide i really appreciate:

The query says :

SELECT ... FROM dbo.DPAGODOCUMENTO AS T2 (INDEX=PK_DPAGODOCUMENTO) RIGHT OUTER JOIN dbo.MDOCUMENTO ... WHERE ...

where PK_DPAGODOCUMENTO is a CONSTRAINT [PK_DPAGODOCUMENTO] PRIMARY KEY CLUSTERED on the table [DPAGODOCUMENTO]

what really means the part "(INDEX=PK_DPAGODOCUMENTO)" and what it does, we are using MSSQL 2005, thanks in advance guys.