GSM-P(rimary) is a term used to denote the primary band for GSM. The primary band ranges from 890 - 915 MHz paired with 935 - 960 MHz. Mobiles transmit in the lower of the two bands, base stations transmit in the upper band.
In this band are 124 channels from 200 kHz defined.
The primary band has been extended later, see E-GSM. Nowadays, there are also a number of other bands used for GSM. Of these, the 1800 MHz band (GSM1800) and the 1900 MHz band (GSM1900) are used most.
The band is also referred to as P-GSM.