TLM1 AND TLM 2

can anyone tell me
why mentioning tlm 1 as pass by value and tlm 2 is pass by refernce .I am understood tlm concepts but what pass by value and pass bby refernce in tlm

In reply to Om Ganesh B k:

Please explain where you are seeing this terminology to give us a context to what it might be referring to.

While Reading difference between tlm 1 and tlm 2 the below definition

TLM1 The TLM1 ports provide blocking and nonblocking pass-by-value transaction-level interfaces.
TLM2 The TLM2 sockets provide blocking and nonblocking transaction-level interfaces with well-defined completion semantics.

In verification academy uvm connect session he mention TLM 2 is pass by reference so i am not getting the actual meaning
https://verificationacademy.com/sessions/introduction-uvm-connect