Gayatrii chanda is a chanda (metre) mentioned in the Vedas. There are few other chandas like gáyatrii, anust́upa, triśt́upa, jagatii, mahatii. This metre has 3 lines, and there are 8 syllables in each line.[1]
References
^Shrii Shrii Anandamurti Ananda Vacanamrtam Part 1