PER: After your final eligibility review is complete at CIO, if successful, you will receive confirmation of positive final eligibility review (PER).
AOR: It means ur file is received at visa office and is put in a queue to be reviewed by visa officer and if found eligible it will undergo further processing. There is a possibility that when they issue an AOR there is also a BF'D(Bring Forward Date) set on that particular file. They also start working on BC once the file is recd which indicates why so many get their MR so quickly.
CAIPS is short for "Computer Assisted Immigration Processing System". It is the computer system historically used by CIC to process visa applications, and holds all the information on the current status of every immigration application being processed by overseas offices (ie. those outside of Canada), other than new applications at offices which have switched to using the "GCMS" system.
GCMS is short for "Global Case Management System", and is the newer computer system that CIC is rolling out across their offices around the globe. Once fully incorporated it would supersede CAIPS & FOSS; and manage all info under one umbrella - Mother of All. It's still under implementation in many overseas CHCs. It was expected to be fully operational by 2012.