they can. when we are talking about parallel, it can be concluded into 2 situations, the parallel of straight lines and the parallel of curves. the situation of straight lines is just a particular example of paralle.
there are many example of parallel of curves, for example, concentric circles, tortuous railway and so on. the essential character of parallel is a certain unchange distance, the concentric circles is a good example of this. at the same time circles are also curves. so curves can be parallel to each other.
circle is made up of infinite points,so Corresponding points of circles are always the same distance apart,then concentric circles are parallel.
I'm sorry,My native language is Chinese,Do I make myself clear?
A parallel of a curve is the envelope of a family of congruent circles centered on the curve. It generalises the concept of parallel lines.