Answer:
The answers are :
1. parallel lines
2. midpoint of a line segment
Explanation:
The mathematical terms that cannot be defined for all cases in a system of geometry are:
1. parallel lines and
2. midpoint of a line segment.
A parallel line cannot be defined as lines do not occupy any space. It is a straight one dimensional figure with no thickness and it extends infinitely in both directions.
The points also do not have any dimension like length, area, volume etc.