The phrase "a sight for sore eyes" means something or someone that is a welcome and pleasant sight, especially after a period of not seeing them or after seeing something unpleasant. 

The origin of this phrase can be traced back to the 18th century, and it is attributed to the famous Anglo-Irish writer Jonathan Swift. The phrase is first recorded in a work by Jonathan Swift, known for his satirical writings such as "Gulliver's Travels." Swift used the expression in a letter dated 1738, where he wrote: "

The sight of you is good for sore eyes." This usage by Swift indicates that even at that time, the phrase was meant to convey a sense of relief and pleasure at seeing someone.