https://medium.com/hd-pro/foldable-phones-the-samsung-galaxy-fold-review-ebfa783582ff

Samsung Galaxy Fold (Source Samsung)The Samsung Galaxy Fold introduced at MWC (Mobile World Congress) 2019 was set to launch in late April 2019 (it had been canceled) to much hype. It was not the first form factor to introduce a foldable design, but one of the early ones. It also has competition from Huawei and Royolle, both smartphone makers as well. I was not too excited at first because I wasn’t a fan of the idea. Then the more you read about it, and then finally see a demo, you start to think it does appear to be useful. Folding makes sense when you want a smaller display that can later be made bigger. It is basically a smartphone that folds out into a tablet. The concept looked promising so it was made available to early tech reviewers.

The concept is quite unique. It introduces a new form factor that can fold into the pocket. The Galaxy Fold was meant to be used as a smartphone and a tablet, though it appears users will use it more as a tablet. There are actually two displays on the Galaxy Fold. The outer display is a 4.6" HD+ Super AMOLED panel with a 21:9 aspect ratio. The inner/main display of the Galaxy Fold is a large 7.3" QXGA+ Dynamic AMOLED panel with a 4.2:3 aspect ratio.