- irdome
- IR drop
- IRE
- I-regular group
- Ireland
- Irenaeus
- Irene
- Irene Joliot-Curie
- Irene Papas
- IRF
- IRFA
- IR fluorescent photography
- IRFPA
- IRFS
- iridescence
- iridium
- Iridium-192 radiation source in industry
- iridium anomaly
- iridium satellite
- Iridium satellite constellation
- iridocyte
- iridoid
- iridovirus,iridoviruses
- IR image converter
- Irina Grekova