Using the triangle midsegment theorem to find the missing midsegment

The video tutorial explains the Midsegment theorem, which is similar to the mid 7th theorem for trapezoids. It highlights the conditions under which the theorem is applicable, specifically when lines are parallel and a midsegment is present. The tutorial demonstrates how to apply the theorem to calculate segment lengths, using an example where the midsegment is half the length of the opposite base. The example involves calculating half of 30, resulting in 15.

What does it mean for lines to be parallel in the context of the midsegment theorem?

Explain why the midsegment theorem is applicable in this case.