Hope the below documentation helps you.Its simple and straight.
Terminal Conversation takes place in 2 ways.
A mode of dialogue between program and terminal based on a combination of sending message and receiving message within the same task.
Since human response is slower than the CPU speed, a significant amount of resource will be wasted just waiting .
A mode of dialogue between program and terminal which appears to the operator as a continuous conversation but which is actually carried by a series of tasks
Multitasking CICS allows multiple transactions (tasks) to
execute at the same time
Multithreading CICS allows multiple concurrent tasks to share
the same program
Re-entrant Programs running under CICS do not change themselves so that they can continue from where they left off after an interruption
Conversational Transaction ? Example
EXEC CICS RECEIVE ---- <= TSK1, 12345
EXEC CICS SEND ----- <= EMP(12345) Details
* - - - - - - Program Waits For Response - - - - -
EXEC CICS RECEIVE ----- <= User Enters Data
EXEC CICS RECEIVE
EXEC CICS SEND
EXEC CICS RETURN