These traits are referring to wild specimens of the platy and swordtails. If you look at most of the wild varieties of Xiphophorus hellerii, males tend to have 3-5 vertical thin lines on both sides of the chest. The more intense the thin lines are, the more appealing they are for females. But there are more wild swordtail species besides the Xiphophorus hellerii that have stripes on both sides of the body.
Vertical striping also occurs in a number of wild platies (so, not all), wether that might be Xiphophorus maculatus, Xiphophorus variatus or another wild platy species. They're more present in males than in females. It's one of the traits they have to attract a mating partner.
But there are also fancy varieties that have broader stripes on both sides of the total body, like bleeding heart platies for instance. We would call that vertical barred.
Overhere male Xiphophorus multilineatus (another wild swordtail) that is vertical barred. So, vertical stripes on both sides of the total body.

Overhere two wild platies that are vertical barred.

Overhere a swordtail with vertical lines (not very clear on this specimen but they're present).

And overhere a vertical barred wild platy.
![IMG_0834[1].jpg IMG_0834[1].jpg](https://www.fishforums.net/data/attachments/143/143637-1af192fd0dad4d70d768b47e25808fd0.jpg)
Stripe sided means the horizontal stripes or lateral lines on both sides of the body.
Overhere horizontal stripes (lateral lines) on a Xiphophorus variatus.
Overhere some swordtails with one or more lateral lines.

Overhere a vertical striped platy.
