Why we use the term bandgap in BGR?

in "bandgap reference circuit" name why we use the term bandgap.

BGR -- question

Ref acheived with negative temperature coefficient of Vbe with the positive temperature coefficient
of the thermal voltageVT. The temperature coefficient of at room
temperature, is - 2.2 mV/°C; while, the positive coefficient of the thermal voltage VT
is 0.086 mV/°C. Therefore, a full compensation at room temperature is
obtained by combining the term with positive temperature coefficient and the
one with negative temperature coefficient to give
where m must be equal to 25.6 (=2.2/0 086).

VBG=Vbe+m*VT

Since the value of for low currents
is close to 0.65 V, and at room temperature
is 25.8 mV, the value of
according to KT/q, is 1.31 V. Such a
value is just slightly more than the silicon
energy gap (expressed in volts it is
1.21 V). Therefore, we normally call the
circuits that achieve temperature compensation
band-gap reference