GCSE Biology

What is the difference between specialisation and differentiation in Biology (apparently they mean different things but I thought the terms mean the same thing)?

Remember that your stem cells are undifferentiated cells
Stem cells can differentiate by switching on/off their genes to become a specialised cell.
A specialised cell is adapted to its function - for example erythrocytes do not have a nucleus, for gcse, the reasoning is to have more space for haemoglobin.

So a stem cell differentiates to become specialised.
Differentiation is the process
Specialised (cell, or function) is the outcome