Here are some points which are useful in understanding process, process tree, and address space:
1) A program is an instance of a program in execution.
2) A process has the information which is required to run a program.
3) Information which is related to processes is stored in a process table.
4) When a process is suspended, related pointers which can be used to restart the process is saved by the operating system. A suspended process has the address space and its entry in process table.
5) Communication between processes is known as inter process communication.
6) Process tree: A process can create more processes. These created processes are arranged in a tree hierarchy and are known as child processes.
7) A process has a UID (User Identification) of the user who started the process.
8) A process is an abstraction of a program which is running.
9) A process is used for concurrent operations in a single CPU.
10) By using a process a physical CPU is converted to many virtual CPUs.
11) Address space: Every process has an address space which is a list of memory locations from 0 to a maximum value. A process can read and write in this address space. For a computer which has 64 bit address, then address space would be 2 pow(64) bytes.