This is the 1114th most frequent Russian word.
треть
"Треть" means "one third" in English.
'третье' refers to ordinal rank, meaning third as in sequence.
Он занял третье место в соревновании.
He took third place in the competition.
'треть' refers to a fraction, specifically one third.
Нам нужно разделить это пирог на три трети.
We need to divide this pie into three thirds.
'треть' refers to a portion, specifically one third of a whole group.