火星文 [－－－]

Jyutping fo2 sing1 man4
Pinyin huǒ xīng wén

Definitions (CC-CEDICT)
  1. lit. Martian language
  2. fig. Internet slang used to communicate secret messages that the general public or government can't understand
Definitions (粵典–words.hk)
  1. 名詞
    聽​唔​明​嘅​語​言​、​睇​唔​明​嘅​文字
    unintelligible language; literally: Martian language
Definitions (Wiktionary)
  1. noun, Internet
    Martian language, a style of writing in which Chinese-language text is represented by a variety of scripts and symbols, popular among some young people.