UID is the user ID, PID is the process ID, PPID is the parent process ID.
UID
UID UID (User Identification) of the abbreviation. After UID user registration, the system will automatically give you the value of a UID. This means that users to compile a number.
PID
PID (Process Identification) operating system refers to the process of identification number, which is the process identifier. Each operating system to open a program creates a process ID, a PID. PID (Process control characters) English called the Process Identifier. PID is the code name of each process, each process has a unique PID number. It is the process of allocating runtime system does not represent a special process. At runtime identifier PID will not change, but after the termination of the process identifier PID system will be recovered, it may continue to be allocated to the new program run.
Just run a program, the system will automatically assign an identity. Is the only temporary: When the process is aborted, this number will be recycled, and may be assigned to another new process. As long as no other programs running success, the PID will continue to be assigned to the current program to be run. If you run a successful program, and then run another program, the system will automatically assign another PID.
PPID
On behalf of the current process of the parent process ID;