我的offer里边的一句话，不是很清楚，帮帮忙

我申请Phd的，女王大学给我了一个Higher degree by researh 的offer.
给我的解释是
Candidates are not accepted initially to a PhD (see point 3 of the
guidance notes).  You have been accepted for admission as a research
student with a view to proceeding to a PhD if you perform well enough in
your studies.  
到底是什么意思呢？
其它学校给我的offer直接就写着Phd offer，到底有什么不一样呢？