Hi,

PSUs (Public Sector Undertakings) are Government firms usually owned by Union Government of India or State Government . In short these Government companies behave like private firms and share their profit with the Government. These were set up to accelerate the economy rate and generate employment opportunities in India

They are classified into 4 types based on investments:

(A)Maharatna

(B)Navratna

(C)Miniratna Category-I

(D)Miniratna Category-II

But just by cracking gate you can't get a PSU job, for getting a job in PSU you must get under 500 AIR rank in GATE if you're from general category, Sometimes under 1000 rank may also get selected in Psu depends upon number of vacancies in that year.