User interface
Software
Software and program is exactly the same. The most common is software but some people like to use the term, program.
A program or software that is free to share.
Another term for a computer program is software.
Application software is a term used in the Information Technology industry to describe any software program designed to perform a particular task for the client.
In software engineering, the term porting is when one changes the format of a program. The reason that this is done is for a software or hardware program to work with something other than what it was originally was created for.
There is no one SETI program. The name is a collective term for act ivies that search for intelligent extraterrestrial life. SETI stands for Search for Extraterrestrial Intelligence.
Forests, is the collective term for groups of treed vegetation.
A word processing program (specific application) is application software (generic term).
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App is short for application. In other words, a software program.
nothing, they are different names for the same thing (computer program is the older term, going back to ENIAC in 1945 and probably some earlier electromechanical computers like the Harvard Mark I).