Initialism of in-school suspension.
"The principal decided to send the disruptive student home from class and assign them ISS instead of expelling them."
In plain English: ISS stands for International Space Station, which is a large laboratory orbiting Earth where astronauts live and work together.
"I think he is just experiencing some iss with his computer today."
Initialism of International Space Station.
"The astronauts on ISS conducted several experiments before their return to Earth."