What does the (+) operator mean in sql queries?

Hello,

I have a query which is this:

SELECT supplier.id
FROM supplier, order
WHERE supplier.id = order.suppid (+)
AND order.suppid IS NULL;

I'm curious as to what the (+) is for in the query. I'm new in a job which uses alot of oracle and i'm just starting.

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Thanks lots


Sorry for C/P not sure where to post.