Examining Process Resource Usage - top

top
interactive, shows Process ID, process owner, priority, memory and CPU usage, and command name.

Top shows threads rather than processes - each thread of a process is running in the same virtual memory.
Useful keys:
space = update screen immediately
q  = quit
u  = show only processes belonging to one user
P  = sort by process CPU usage
M  = sort by memory in use
h  = get help on all the key shortcuts