background character; nameless minor character
Used in manga, anime, and light novels for characters who appear only briefly or have no real role. Often implies the character is unimportant or disposable.
mob; weak enemy; minor enemy
Video game term for non-player enemies that are easy to defeat and appear in groups. Also used figuratively for any weak opponent.
The background characters in that anime get defeated right away.
He always plays only minor, nameless roles.
The mobs in this game give little experience.
Let's take out the minor enemies before the boss.
Standard kanji-katakana spelling; 雑魚 means 'small fry' and キャラ is short for キャラクター.
All-katakana spelling, common in manga, games, and casual online writing.
Compound of 雑魚 (zako, 'small fry, weakling') and キャラ (kyara, abbreviation of キャラクター 'character'). The term originated in otaku and gaming culture and spread to general slang.