Tri
Tri- is a numerical prefix meaning three.  Tri or TRI may also refer to:

Places
Tri-Cities Regional Airport, Tennessee, US, IATA code TRI
Triangulum constellation, astronomical abbreviation Tri
Trinidad and Tobago, UNDP country code TRI

People
Tri, Former nickname for wrestler Triple H
Tri Hartanto, Indonesian basketball player

Arts, entertainment, and media
Tri (album), by Ana Stanić
Tri (novel), a Slovenian novel
El Tri, Mexican rock group

Organizations
Taipei Ricci Institute, an educational institute in Taiwan
Tamalpais Research Institute, a virtual music venue, San Rafael, California, US
Translational Research Institute (Australia)
Transport Research Institute, in Scotland

Other uses
AC Tripoli, a Lebanese association football club
Total return index
Toxics Release Inventory, US
El Tri or El Tricolor, nicknames of the Mexico national football team
Triangular function, tri(t)
Trichloroethylene
Triple reuptake inhibitors