Hey,

*PSU stands for Public Sector Undertaking* or Public sector units. These are the units owned by the government of India. PSUs offer various job opportunities to deserving graduates/engineers.
•Eligibility -: Age limit for PSU jobs is 25-28 years.
Applicant must be a graduate.

•Some PSUs organizations conduct their own entrance exams. Entrance exams then followed by group discussion and personal interview.
•And there are certain PSUs such as NTPC, BEL, BHEL which do not conduct their own entrance exam but hire candidates via their GATE performance, clearing the GATE exam is the compulsory criterion for these units.
Here you will find everything about 
PSU -: 
https://www.google.co.in/amp/s/engineering.careers360.com/articles/psu-recruitment-through-gate%3famp

Hope it helps!