What does (+) mean in SQL?

Question

What does the (+) mean in the Where Clauses in this SQL statement?

SELECT  p.FIRSTNAME,
        p.LASTNAME,
        p.LOGINNAME,
        a.DESCRIPTION,
        a.PERIPHERALNUMBER,
        a.SUPERVISORAGENT,
        t.ENTERPRISENAME,
        t.DIALEDNUMBERID,
        sp.FIRSTNAME AS SUPER_FIRSTNAME,
        sp.LASTNAME AS SUPER_LASTNAME,
        sp.LOGINNAME AS SUPER_LOGINNAME,
        sa.PERIPHERALNUMBER AS SUPER_PERIPHERALNUMBER,
        sa.SUPERVISORAGENT AS SUPER_SUPERVISORAGENT,
        a.SKILLTARGETID,
        a.PERSONID,
        t.AGENTTEAMID,
        sa.SKILLTARGETID AS SUPER_SKILLTARGETID,
        sa.PERSONID AS SUPER_PERSONID
FROM    C2O.AGENT a,
        C2O.PERSON p,
        C2O.AGENT_TEAM_MEMBER tm,
        C2O.AGENT_TEAM t,
        C2O.AGENT sa,
        C2O.PERSON sp
WHERE   a.PERSONID = p.PERSONID
AND     a.SKILLTARGETID = tm.SKILLTARGETID(+)
AND     tm.AGENTTEAMID = t.AGENTTEAMID(+)
AND     t.PRISUPERVISORSKILLTARGETID = sa.SKILLTARGETID(+)
AND     sa.PERSONID = sp.PERSONID(+)
AND     a.DELETED = 'N'
AND     p.LOGINENABLED = 'Y'
AND     SUBSTR(a.PERIPHERALNUMBER,2,3) = 580;

Answer 1

In Oracle, the (+) specifies that the join is an outer join (instead of an inner join as this implicit join syntax usually implies).

Making it an outer join means that the row should be included in the results even if that particular item is null.

Answer 2

In Oracle SQL, this is the deprecated outer join operator.