a loop: one of the yarn eyes sewn along the edge of a tabernacle curtain, which a clasp was pushed through to join two panels
This word names one small fitting from the tabernacle, and it is used nowhere else in the Bible. Each loop is an eye of yarn worked into the edge of a curtain panel, and the clasps (קֶרֶס) were brought through it so that two halves of a covering hung together as one piece. The word only ever appears in the plural, "loops", because the loops are always made in matched sets rather than one at a time.
Every occurrence sits inside the same building account, first as the instructions given to Moses in Exodus 26 and then as the report that the work was carried out in Exodus 36. The details repeat almost word for word: fifty loops along the edge of one panel and fifty along the edge of the panel it will meet, set so that the loops line up directly opposite one another (Exodus 26:5; Exodus 36:12). The inner linen curtains were given loops of blue yarn (Exodus 26:4; Exodus 36:11); the goat hair covering stretched over them was given loops too, with no color named for them (Exodus 26:10; Exodus 36:17).
The loop is the fabric half of a two part fastening, and it does nothing on its own. Only when the metal clasps are brought into the loops does the text state the result: the tent "shall be one" (Exodus 26:11). A modern reader can skim a word like this as mere hardware, but in this account the plain, exact workmanship is what turns a pile of separate panels into a single dwelling.