Posted in Government & Military, Internet Slang, Schools & Education YSI stands for Yousendit (File Transfer Website) YSI stands for Young Sustainable Impact (Norway) YSI stands for Youth Service, Inc. (Philadelphia, PA) YSI stands for Yellow Springs Instruments (Yellow Springs, OH) YSI stands for You Said It YSI stands for Young Social Innovators (Ireland) YSI stands for Youth Science Institute YSI