Simplify the following text for a Grade 6 native English-speaking person.
Original: The origin of the railway 's name is uncertain : it may refer to the parish of Talyllyn , which contains its eastern terminus , or it may come from Tal-y-llyn , a large glacial ribbon lake at the foot of Cadair Idris 3 m further east .
Simplified: Tal-y-llyn is a large glacial ribbon lake at the foot of Cadair Idris 3 m further east .