This is the 3441st most frequent Japanese word.
片方
"One side" or "one counterpart."
In this sentence, "片方" is used to indicate one piece out of a pair, specifically one of the gloves.
彼は片方の手袋を無くしました。
He lost one of the gloves.
Here, "片方" is used to refer to one side of items typically used in pairs, in this case, earphones.
イヤホンの片方が壊れています。
One earphone is broken.
This sentence uses "片方" to specify one shoe out of a pair of shoes.