Say someone wrote you an email, and, being the dilligent Japanese language student you are, you’ve just been too busy practising your kanji to write back to them. When you finally emerge from under piles of practice sheets covered in 21-stroke mini-nightmares, you go to reply to the email, but you feel bad for taking so long to get back to the person. What do you say in this case?
返事が遅くなり、申し訳ございません （へんじがおそくねり、もうしわけございません） is perfectly acceptable, if very polite.
If it’s someone you haven’t talked to in a while, ご無沙汰しています （ごぶさたしています） is something you could possibly say.
But say it’s a good friend you’ve known for a while, and you also happen to feel like showing off your knowledge of Japanese slang a bit. You could say…
亀レスごめん （かめれすごめん） / 亀レス失礼します （かめれすしつれいします）
亀レス is an interesting bit of Japanese slang that evolved in the last few years to mean “replying to someone’s email after a long delay”.
Broken down, 亀（かめ） is the Japanese word for turtle. Clearly something slow!
レス is the shortened form of レスポンス – response.
亀レス, therefore, is a response as slow as a turtle! We’ve all been there…
Stay turned for more interesting Japanese!