Depends on the context. Literally, it means "write a word less", Figuratively, it means "you are too verbose/convoluted in your writing".

少+verb，do somethings less，for examples: 少吃饭 eat less 少买一件衣服 buy one clothes less 少喝酒 drink less wime 少写一个字 write a word less. 多+verb，do somethings more,for example: 多睡觉 sleep more 多睡一个小时 sleep one more hour 多喝水 drink more water 多喝一杯水 drink an extra glass of water

谢谢

Means you missed one word by mistake when writing a sentence.