When they refer to a travel document do they mean a passport?

In most cases, yes... but it can also be in place of a passport in some situations. Travel documents may also include any visas you may need... student visa, any that may be required by a particular country. In some cases, if this is for attending university, you may be asked to show an acceptance letter from the university as well.
If this is for university, you can find out exactly what you need by contacting the university.