GSM (g/m²)
GSM measures a textile's mass per unit of area, in grams per square metre (g/m²). It is the number-one indicator of a terry fabric's density: a 400 g/m² towel is light and quick-drying but absorbs little; 550 g/m² — the hotel standard — hits the softness/absorbency/drying balance hotels and guesthouses look for; above 600-700 g/m² you are in spa and bath-mat territory.
Flat linen (sheets) reads differently: quality there comes mostly from the density of the weave's threads. Remember: g/m² to judge terry, thread count to judge a sheet. Our 70×140 towels are 550 g/m², our bath mats 700 g/m².
And in Arabic?
الوزن بالغرام للمتر المربع (غ/م²) — مقياس كثافة الفوط
To go further