Most likely is Big for Dates, meaning that the pregnancy may be further on than they thought, or that it's going to be a big baby. Your friend can always ring her midwife and ask for an explanation of the scan - far better to ring than to worry.
BPD stands for Bi-Parietal Diameter. It is a measurement between The 2 Parietal bones of the skull and is an indication that the baby is growing as he or she should.