| Instructor Rating System | Academic & Science |
| Intelligent Responsible Students | Academic & Science |
| International Relations Society | Academic & Science |
| Illinois Reading Society | Academic & Science |
| International Reference Star | Academic & Science |
| Individualised Research Study | Academic & Science |
| Société Internationale Renardienne | Academic & Science |
| International Reynard Society | Academic & Science |
| Irreverent Rodent Society | Academic & Science |
| Interesting Readers Society | Academic & Science |
| Internal Revenue Service | Accounts and Finance |
| Increasing Returns To Scale | Accounts and Finance |
| Sturgis (mi) | Airport Code |
| Investor Relations Society | Associations & Organizations |
| Indian Register of Shipping | Associations & Organizations |
| Institute of Regional Studies | Associations & Organizations |
| Irsa Inversiones y Represent | Business |
| Inventory and Resource System | Business |
| Independent RV Sellers | Business |
| Internal Regulating Services | Business |
| Instant Refund Station | Business |
| Information And Referral Services | Business |
| Identify, Reduce, and Schedule | Business |
| Indoor Residual Spray | Chemistry |
| Italian Rhythm Section | Community |
| Interested Readers' Society | Community |
| Irwin R. Scheister, wrestler (real name: Lawrence Michael Rotunda) | Community |
| Intermediate Reference System | Computer and Networking |
| Interchange Recors Separator | Computing |
| It Really Stinks | Computing |
| Intelligent Register System | Computing |
| Image Results and Security | Computing |
| International Rongdoing Society | Computing |
| Infra Red Sensor | Computing |
| Interchange Record Separator | Computing |
| International Retail Service | Computing |
| Initial Receive Sequence | Computing |
| Intel Real Sense | Computing |
| Information Retrieval Service | Computing |
| Internet Radio Station | Computing |
| Inter-Domain Routing Security | Computing |
| Indian Remote Sensing | Earth Science |
| Infrared Spectroscopy | Electronics |
| Resource (wordperfect) | File Type |
| International Riot Society | General |
| Infernal Revenue Service | General |
| Iron Ring Stag | General |
| Income Revenue Service | General |
| Irate Raging Spouse | General |
| Improving The Republican Summer | General |
| Information Retrieval System | General |
| Inserted Rectally Service | General |
| Instinctive Reaction To Struggle | General |
| Interesting Rural Scenery | General |
| International Responsibility Seminar | General |
| I Remain Standing | General |
| International Revange Service | General |
| Instant Recreational Satisfaction | General |
| Integrated Reception System | General |
| Internal Revenue Selfies | General |
| Increased Rotational Speed | General |
| Indian Readership Survey | General |
| Internal Revenue Services | General |
| Insensitive Ruthless Shysters | General |
| inverse Raman scattering | General |
| Information and Reporting Services | General |
| Internal the R Stands | General |
| Innovative Reflection Spotlight | General |
| I Ride Slow | General |
| Insulin Receptor Stke | General |
| Inmate Roommate Soulmate | General |
| It's Really Stealing | General |
| Intrapulse Raman Scattering | General |
| Invisible RattleSnakes | General |
| Implicit Radiation Solver | General |
| Independent Rear Suspension | General |
| Integrated Restraint System | General |
| Infrared Locking System | General |
| Illini Racing Series | General |
| Inflatable Restraint System | General |
| Intelligent Radar Sensor | General |
| Intelligent Road Studs | General |
| Impreza Rs | General |
| International Relief Service | Governmental |
| Inhibit Republican Speech | Governmental |
| Indian Residential Schools | Governmental |
| Identical, Related, or Similar | Governmental |
| Incident Reporting System | Governmental |
| Indian Revenue Service | Indian Ministry of Finance |
| International Rod Society | International |
| International Revenue Service | International |
| I'm Really Sexy | Internet |
| It's Really Sexy | Internet |
| I'm Really Sweet | Internet |
| Institutional Representatives | Jobs |
| Inverse Repeated Sequence | Maths |
| Isolation Resistance Sanitation | Medical |
| Insulin Receptor Substrate | Medical |
| Insulin Resistance Syndrome | Medical |
| Irritable Rabbit Syndrome | Medical |
| Internal Responsibility Syndrome | Medical |
| Irritable Ricky Syndrome | Medical |
| I Respect Someone | Messaging |
| Intimate Relations Schedule | Messaging |
| Interface Requirements Specification | Military and Defence |
| Information Reporting System | Military and Defence |
| In Range Shooting | Military and Defence |
| Information and Reconnaissance Ship | Military and Defence |
| Indoor Residual Spraying | Real Estate |
| Inertial Reference System | Space Science |
| Internet Racer's Supply | Sports |
| Interest Rate Swap | Stock Exchange |
| Kirsch Municipal Airport | Transport & Travel |
