I would appreciate an explanation between these two terms.
I am doing some remote work while I do some traveling. Normally, when I work from home my VPN connection uses the IPSecOverNatT Protocol when I view the current VPN connections through ASDM. I am currently on a University campus and my connection is now just the plain IPSec protocol. What causes this change and what is the change?
It will only use NAT-T (UDP/4500) if the path has PAT configured. Because the plain IPSEC (ESP) is a protocol, not a TCP or UDP with port number, it can't pass through a PAT device, therefore during the IPSEC negotiation, if it detects there is PAT in the path, it will use NAT-T. Otherwise, it will just use the plain ESP packet.
Hope that answers your question.