There have been a number of complicated terminologies in the Resident Evil canon, so many that it may be hard to keep up with them all. Here's a list of some of the most commonly used words, names, and acronyms.

Umbrella Corporation

The evil pharmaceutical corporation that started the whole Biohazard mess. Umbrella was founded by three college friends in the 1960s and became world famous under the guise of a pharmaceutical and technological research conglomerate. They had multiple company branches and research facilities all over the world, secretly engaged in grotesque viral experiments on human test subjects, creating undead monstrosities for the purpose of chemical and biological warfare on the black market, including super soldiers. They were eventually exposed and shut down by Jill Valentine and Chris Redfield.

R.P.D.

Raccoon Police Department. During the Raccoon City outbreak, the police station served as a last safe haven against the hordes of walking dead, until the insane Police Chief Brian Irons slaughtered the survivors barricaded within. Irons had taken bribes from Umbrella during the city's creation, turning a blind eye to their illegal activities and the construction of their secret subterranean labs. The last known R.P.D. recruit was Leon Kennedy, who arrived for his first day on the job just as the outbreak spread across town.

S.T.A.R.S.

The R.P.D.'s elite field agent force, the acronym stands for “Special Tactics And Rescue Service.” The S.T.A.R.S. were divided into two teams, Alpha and Bravo. Bravo Team consisted of Richard Aiken, Edward Dewey, Enrico Marini, Kenneth Sullivan, Forest Speyer and Rebecca Chambers—none of whom were apparently good at their job. The entirety of Bravo Team (except Rebecca) was slaughtered in the Arklay Mansion outbreak. Alpha Team, consisting of Chris Redfield, Jill Valentine, Barry Burton, Joseph Frost, Brad Vickers, and team captain Albert Wesker, were dispatched to rescue Bravo Team. Of course Wesker, an Umbrella agent, lured his teams into the middle of the mansion outbreak so as to test the viral creations in a battle scenario. Frost was killed in the mansion and Vickers later died in the Raccoon City outbreak. Jill, Chris, and Barry quit S.T.A.R.S. after the Mansion Incident to pursue Umbrella as independent agents. The location of Rebecca currently remains unknown.

B.O.W.

“Bio-Organic Weapons” is the umbrella term* for the monsters that crop up during the Resident Evil series, including unexpected mutations, secondary infections, and transmissions of viruses. The term has been adopted by the rest of the world by the time RE6 takes place. Basically, this applies to zombies, mutants, Plaga hosts, and anything else that can potentially be created through a controlled infection or implementation and used in a war zone to either kill other humans or turn them into its more B.O.W.s.

*See what I did there?

U.B.C.S.

The Umbrella Biohazard Countermeasure Service. In dealing with medical research, Umbrella kept up public appearances by recruiting and maintaining a squad of armed forces for dispatch into biohazard contamination zones. They were trained to search and rescue civilians and protect them from potential chemical warfare threats, with a priority given to Umbrella researchers and employees. Due to the extremely dangerous nature of their work, many of the operatives were drafted from prisons, and the option to join the UBCS was sometimes an alternative to death row. Within each unit, specially trained squad members were secretly placed to collect data on any B.O.W.s encountered by the UBCS, preserve samples of viruses, and destroy evidence that tied Umbrella to the outbreaks.

B.S.A.A.

The Bioterrorism Security Assessment Alliance, founded by Chris Redfield and Jill Valentine in 2003 after the downfall of Umbrella. Backed by the Global Pharmaceutical Consortium (the group responsible for shutting Umbrella down), the BSAA travels the globe to investigate bioterrorism claims and control biohazard threats. The agents are specially trained to deal with B.O.W.s of all kinds and prevent their spread. It is the members of the BSAA who board the SS Queen Zenobia in Resident Evil Revelations to investigate the mysterious bioterrorist group Il Veltro. The BSAA has divisions around the world—Josh Stone and Sheva Alomar are members of the West African division.

Tricell

Tricell Incorporated is a rival pharmaceutical/technology firm that bought out Umbrella’s assets following that company’s dispersal. While it, like Umbrella, has many worldwide branches, the African branch—headed up by the beautiful Excella Gionne—has taken up Umbrella’s cause, creating new strains of Plaga parasites. With the help of Albert Wesker and data on the Progenitor virus, Tricell also developed the Uroboros virus which, like the T-Virus and Progenitor viruses before it, kills the vast majority of its hosts.