What Is Transaction Processing System In DBMS?

It is a unit of program to perform a specific task
for eg.
  To transfer amount Rs 1000 from account A to B the transaction is
read(A)   -- get the current bal of A
A:=A-1000     -- debit Rs 1000 from A
write(A)   -- update the bal of A
read(B)   -- get the current bal of B
B:=B+1000   -- add Rs 1000 to B
write(B)   -- update the bal of B