It means "nothing special". The expression comes from when you are on holidays or away, and telling everyone at home how great things are. The scenery is great ! The people are great ! etc, etc. 'Nothing to write home about' is the negation of 'wanting to write home'. Rather than being special, things are average, nothing special. Nothing special or out of the ordinary to write home or tell people about. So used by itself, it means 'nothing special'/'no big deal'/'nothing to get excited about'. Examples: "I went to the that new museum, but it was nothing to write home about". ie. The museum was nothing to get excited about. It was nothing special. "The restaurant we went to was ok, but nothing to write home about". ie. The museum was ok, but fairly ordinary. There was nothing that great about it.

The idiom is used to refer something which is not very interesting or exciting.The term was common in the world war-1 among overseas troops . You can use this idiom to indicate or express anything that is not impressive or interesting or important. Examples: a) we went to a new restaurant in Paris but nothing to write home about it.Explanation-Though the restaurant was new, it was ordinary not especially impressive. b) I read a detective book in the morning but nothing to write home about this.Explanation: The book was not interesting or exciting.

It means the same as: Not worth mentioning Nothing to get excited about Not a great achievement. "Did you see the Lizzo Concert" "Yeah" "Was it great?" "Nah. Nothing to write home about"