PO stands for probationary officer as designation Probationary Officer holds (PO) in banks - The IBPS PO work profile includes holding the designation of an Assistant Manager (AM) on Probation. He is in Junior Management Grade-1 (JMG-Scale 1) Officer thus he/she is often called as Scale 1 Officer or Asst. Manager.

Also there are various exams for PO like IBPS, SBI and private banks can also recruit for this post through entrance.

Hope this helps!!!