Its Stuck: ps and kill
Every now and then a program is running that just doesn't seem to be doing anything or worse, it is consuming lots of resources doing something you hadn't intended (computers have an annoying habit of doing exactly what you tell them to do rather than what you wanted them to do). Unlike other operating systems where your only recourse might be to turn it off, UNIX assumes this would adversely impact other people on the system and provides an alternative.
You can try control-C (process interupt), control-D (another kind of interupt), or control-Z (put it to sleep--but it'll still be there doing nothing).
First you need to find the process id number.
Use ps -U YourUserName to get a list of processes you're running. You'll likely be surprised at the number of things you're doing. Look for the name of your stuck program on the right most column and then note the process id number listed in the left most column.
Now nuke it using kill pid where pid is the process id number. Still didn't die? Try kill -9 pid to let the computer know that you're really serious about it.
But what if the ps command showed more processes that could fit on the screen and they just flew past. A good time for a pipe to slow things down: ps -U YourUserName | more