Similar to previous cellular generations, the 5G spectrum is divided into multiple frequency bands. Although this time around, 5G aims to use vastly more spectrum than ever before. On the one extreme, we have millimeter waves (often referred to as mmWave) and, on the other, frequencies that lie in the sub-6GHz spectrum. Both are key parts of 5G deployments, yet offer vastly different benefits and drawbacks.
In the past, you really had little choice when picking 4G capabilities between phones. Even today, inexpensive smartphones offer comparative LTE speeds as a more premium device, everything else being equal. With 5G however, we now have two distinct frequency ranges that work very differently from one another.