The word sindon, according to The International Standard Bible Encyclopedia By Geoffrey W. Bromiley, is a linen cloth of fine quality. He writes:
The young man who fled naked on the night of Jesus' arrest had worn only a linen tunic or sheet (Mark 14:51). In preparation for his burial, Jesus' body was wrapped in a shroud of this material (Matthew 27:59; Mark 15:46; Luke 23:53).
According to biblical and shroud scholar Kim Dreisbach:
The Synoptic Gospels use the word sindon in the singular to designate the Shroud (Matt. 27:59; Mk. 15:46 (twice); Lk. 23:53). Sindon appears only six times in all of the New Testament. In an anecdote unique to Mark, it is used twice in 14: 51-52 to describe the linen cloth left by an unnamed young man when he fled naked from the Garden of Gethsemane.