In computer science, an instance is an occurrence of a software element that is based on a type definition.
Each instance of a class shares a data layout but has its own memory allocation.
A computer graphics polygonal model can be instantiated in order to be drawn several times in different locations in a scene which can improve the performance of rendering since a portion of the work needed to display each instance is reused.
In a POSIX-oriented operating system, program instance refers to an executing process.
It is instantiated for a program via system calls such as fork() and exec().