This question was asked in one of my interview and I was not that knowledgeable to answer it at that time. I don't want anyone else (who learn NSX and my blog. I have no way to share it with all the world:)) to be unanswered on this question. With this thought, I am writing the answer below.
It is very small thing but matter a lot while asked in an interview.
It refers to a set of three and five different values that comprise a TCP\IP connection. It include as shown below.
3-Tuple: The tuple (source IP address, destination IP address, ICMP Identifier). A 3-tuple uniquely identifies an ICMP Query session. When an ICMP Query session flows through a NAT64, each session has two different 3-tuples: one with IPv4 addresses and one with IPv6 addresses. 5-Tuple: The tuple (source IP address, source port, destination IP address, destination port, transport protocol). A 5-tuple uniquely identifies a UDP/TCP session. When a UDP/TCP session flows through a NAT64, each session has two different 5-tuples: one with IPv4 addresses and one with IPv6 addresses.
I hope who didn't know about this, it will add value in them.
Be Interview ready and Always! You never know when you will get golden opportunity and that call,you were waiting for since long.