They are back from the 80's, the crop tops! We've seen this style by Madonna who flaunted her tummy. For those that lived through the 80's, it was one of those trends you supposed to be glad to see the back off. We all know fashion is like a cycle. Everything goes back in trend.
For those who are conservative or if you do want to persist with the trend, you can still pull these off by wearing high waisted pants/shorts, trousers or by double layering with plain tank top (mostly white or black). Mix and match, that's what you must always do for a perfect blend :)