What does the Japanese word Sempai mean?

Answer 1

its sempai and it means person of a high level

for example a grade 8 student would refer to a grade 11 student as sempai

or a judo yellow belt would refer to a green belt as sempai yellow being lower than green

Answer 2

Sempai, also said Senpai, is a honorific for a upperclassman. Someone who is higher in rank than you, such as a collage student if you're in high school, or someone who is at a higher position at a job.
It is spelt "Senpai"

It is what you say to address older students in your school, lets say if you were in the freshman year, juniors and seniors are your senpai.