Ship of Theseus

The ship of Theseus is a question about if you can consider that an object is the same one when you replace parts of it. It is a paradox.
For example, if you have an axe and you replace its handle, it is still the same axe? And if you replace the blade? And if you made another axe with the old handle and blade, the "real" axe is the one that has the replaced elements or the one that has the old ones?
Different people answer this question in different ways.
The name comes from a legend about ancient hero Theseus.