A Gurmata is an order passed by the Sarbat Khalsa

Sarbat Khalsa

Sarbat Khalsa from sarva, a Sanskrit word meaning all or everything, was a biannual deliberative assembly of the entire Khalsa held at Amritsar in Panjab during the 18th century...

 in the presence of the Guru Granth Sahib

Guru Granth Sahib

Sri Guru Granth Sahib , or Adi Granth, is the religious text of Sikhism. It is the final and eternal guru of the Sikhs. It is a voluminous text of 1430 angs, compiled and composed during the period of Sikh gurus, from 1469 to 1708...

. A gurmata may only be passed on a subject that affects the fundamental principles of Sikh religion

Sikhism

Sikhism is a monotheistic religion founded during the 15th century in the Punjab region, by Guru Nanak Dev and continued to progress with ten successive Sikh Gurus . It is the fifth-largest organized religion in the world and one of the fastest-growing...

 and is binding upon all Sikh

Sikh

A Sikh is a follower of Sikhism. It primarily originated in the 15th century in the Punjab region of South Asia. The term "Sikh" has its origin in Sanskrit term शिष्य , meaning "disciple, student" or शिक्ष , meaning "instruction"...

s.
Gurmata is similar to Fatwa

Fatwa

A fatwā in the Islamic faith is a juristic ruling concerning Islamic law issued by an Islamic scholar. In Sunni Islam any fatwā is non-binding, whereas in Shia Islam it could be considered by an individual as binding, depending on his or her relation to the scholar. The person who issues a fatwā...

in the Muslim tradition with a difference that Fatwa is not binding on all Muslims while Gurmata is binding on all Khalsa, it is not binding on non Khalsa Sikhs.