Oracle to PostgreSQL help: What is (+) in Oracle select? - Mailing list pgsql-sql

I'm trying to modify an application which runs on Oracle to run against 
PostgreSQL.  I'm currently stuck on a query that I can't recognize, it 
doesn't look like standard SQL.

A select is done across two tables, however when joining the foreign 
key, the right hand side of the equallity has (+) appended

SELECT o.* from one o, two t where o.key = t.key(+)

Does anyone know what this does and how I can reproduce the select in 
PostgreSQL?

Thanks
Chris