What does it mean that the T-shirt can be worn front-to-back and inside out?

Turning what was the front to the back and flipping what was the outside to the inside are two different choices. This long sleeve from Low Tide was made leaving both of those options open^[1]. As a result, choosing does not end once when you buy it, but happens once more each time you wear it.

When you swap the front and back, the depths of the front neckline and back neckline trade places, and when you turn it inside out, the seams and stitching that were on the inside come to the outside. The material is a rib knit with a subtle sheer quality^[2]. A rib knit is a weave where vertical ribs repeat regularly, so it stretches well sideways to cling along the body, and as it stretches, light can pass through between the ribs. If you are concerned about sheerness, matching the color of the inner layer is the usual way.

hmmm, rather than saying it creates the effect of multiple garments with a single piece, it is closer to a garment where you decide which side to put forward each day.