75 Meters
75 Meters : 3.600 MHz-4.000 MHz, With Phone emissions allowed.
80 Meters: 3.500 MHz- 3.600 MHz CW and RTTY/Data only
80 Meters: Sometimes referred to as the ENTIRE, CONTIGUOUS (U.S.) Amateur allocation from 3.5000-4.000 MHz; including the low end of the 80 Meter Amateur allocation, but including the 'phone portion of the 3.6-4.0 MHz allocation sometimes referred to as "75" Meters.
In the past, many ops referred to "80 Meters" as covering the entire 3.5-4.0 MHz band, as it was a continuous allocation; and since CW was a legal mode across the ENTIRE allocation, many OT's didn't bother with a distinction between 80 and 75 Meters. The real issue sort of was manufactured; because of the low frequency/long wavelengths, the classical "CW" and 'phone allocations DO actually have relatively significant differences in wavelength.
Think of it THIS way:
75 Meters: Phone operation below 4 MHz
80 Meters: May include the CW/Data AND phone operation areas, unless otherwise specified