YSI explained

YSI may refer to:

• YouSendIt, an online site providing sending of large files
• Young Social Innovators, a project-based competition for schools in the Republic of Ireland
• Youth Science Ireland, formerly IAYSG (Irish Association of Youth Science Groups)
• YSI Inc., a brand of sensors and software for Xylem, Inc.
• YSi, a silicide composed of yttrium and silicon
• Parry Sound/Frying Pan Island-Sans Souci Water Aerodrome (IATA code: YSI), a Canadian airport
• YSI Includes created by Y_Less for SA-MP, a multiplayer modification of GTA Sanandreas.