PSI it has several meanings depending on the context in which it is used. The phoneme "psi" corresponds to the twenty-third letter of the Greek alphabet: Ψ
The same Greek letter "psi" represented by the trident is the symbol adopted by Psychology.
PSI is also the acronym for “For Your Information”, usually used in offices or in email messages, when you want to summarize the words to send some information.
Psi for Windows is a system for exchanging me instant messages. It was developed at the beginning to serve the public that uses free software, and now it has a test version for Windows. The program was developed with open-source, allowing for modifications. With Psi, communication takes place in real time, just connect to a local or public server to start conversations.
PSI is also the acronym for “Import Substitution Process”, started in Brazil after the 1929 crisis and which is still in use.
PSI is also a measure of pressure, or pounds per square inch, and the unit of pressure in the English/American system.
PSI was eliminated from Russian spelling along with ksi, omega and yus in the spelling reform of 1708, and it has also been taken from other secular languages, and the only place it is still used is in the Church. Slavonic.