1. What does it mean?
맛저 shortens 맛있는 저녁. Depending on the sentence, it can refer to a nice dinner or wish someone an enjoyable one, as in 맛저하세요.
Also written or said as 맛저하세요, 맛저해, 맛있는 저녁
2. The nuance
It is a light chat sign-off, not a full restaurant order. Adding 하세요 makes the ending polite, but the abbreviation remains casual. In a formal message, 저녁 맛있게 드세요 is a clearer, more complete alternative.
3. Examples
“난 이제 저녁 먹으러 가. 너도 맛저해!”
I'm heading out for dinner now. Enjoy yours too!
“퇴근하신 분들 모두 맛저하시고 편히 쉬세요.”
If you're finished with work, enjoy dinner and have a restful evening.
Sources
KoreanClass101: Korean language lessons
References support the meaning and usage. Example sentences are written for NoCapWiki.