ga·ki /ˈɡa.ki/ · ガキ · 餓鬼
Informal Japanese noun. A bratty kid. Used every day by parents, teachers, siblings, and comedians. Usually affectionate under the complaint.
Gaki (ガキ) means a misbehaving child. It is the word a parent uses when their kid tracks mud across the floor. It is what a comedian calls himself when telling a childhood story. It is the label on a poster for a children's variety show.
Closest English words: brat, rascal, little monster. None map exactly. Gaki is warmer than brat and less quaint than rascal.
The kanji form 餓鬼 also names a Buddhist spirit (the hungry ghost of the gaki-dō realm). That reading is rare in daily speech today. Ask a Japanese teenager what a gaki is and they will describe a classmate, not a ghost.
「あのガキ、また壁に落書きしたぞ。」
Ano gaki, mata kabe ni rakugaki shita zo.
"That brat drew on the wall again."
「ガキの頃はこういうのが好きだった。」
Gaki no koro wa kou iu no ga suki datta.
"When I was a kid, I liked stuff like this."
More examples on the usage page.
For illustration in the same register (Yoshitomo Nara-style portraits, streetwear editorials, candid mischief scenes), see gakistudio.com.