Okay Just,
As I don't see it in this thread I presume you are 'just needing to know' to satisfy your own curiosity or because of a discussion you have heard, or a part of a code or practice for the exams.
So, you need to forgive us and a good many others. The phrase 'in position' will be a term used in many places referring to a down flat weld which if it is a fillet weld in a T joint will actually be a horizontal fillet weld. In that joint the 'T' would be place so each piece forming the joint would be at a 45° angle to get it into the truly 'flat' position which would then be called 'in position'. For a groove weld both members forming the joint would be flat on the table/floor, etc and the groove would be welded with the electrode pointing down into the groove. Again, flat and 'in position'.
So, out of position is any other position; vertical, overhead, or other variants of horizontal which differ from the one that is basically 'flat' for the T joint.
Where in D1.1 is your reference taken from?
Brent