AE = Aviation Electrician' Mate
AT = Aviation Electronic Technician.
AV is not a rating in and of itself - but a community distinction on going in: aviation, surface, etc. The two ratings listed are aviation ratings. Other services use codes called an "MOS" or Military Occupational Specialty. The Navy has a long history of describing career specialists using ratings, and has maintained that. More detail at
http://www.navy.mil/navydata/navy_legacy_hr.asp?id=264
Technically speaking, rank applies to officers, rating to enlisted...That rating is then used within the Navy structure to properly title someone. so, for our Aviation Electrician example:
E-1 Seaman Recruit SR
E-2 Seaman Apprentice SA
E-3 Seaman AESN
E-4 Petty Officer 3rd Class AE3
E-5 Petty Officer 2nd Class AE2
E-6 Petty Officer 1st Class AE1
E-7 Chief Petty Officer AEC
E-8 Senior Chief Petty Officer AECS
E-8 Master Chief Petty Officer AECM
for the OP - I hope you've been through this site:
http://www.bootcamp.navy.mil/