The term "waifu" is a word that is used prevalently in the Manga/Cartoon, and Video-
game fandoms. The origin of the word comes from the katakana word for
wife; ワイフ
However, Japanese-speakers will never use that word. The real word for
wife is 妻 (tsuma/sai).
"Waifu" is used to refer to a fictional
girl or woman (usually in
Anime, Manga, or video-games) that you have sexual attraction to, and you would even marry.
Remember; "ワイフ waifu" and "妻 tsuma" are completely different. Waifu is a joke word that Anime fans call fictional female characters that they love and would marry if they were real. Your tsuma is your real wife. That is the real Japanese word for wife.
Example of waifu:
"Do you like Camilla from Fire Emblem Fates?"
"I LOVE Camilla! Her large breasts, her curves,... she's my waifu!" 😍
(This guy has sexual attaraction towards Camilla from Fire Emblem Fates. He would
even marry her if she was real, he called her his "waifu"
Example of 妻 :
私は今日結婚しました これは私の妻キコです
「I got married today. This is my
wife Kiko.」
(A man was married to Kiko that
day. She is real, not a fictional character. The real Japanese word for
wife was used.