Hello Omkar,
So dear, basically UG stands for Under-Graduate and PG stands for Post-Graduate.
In UG course for engineering, you will get the degree B.tech ( Bachelor of Technology), where as in PG course, you will get the degree M.tech (Master of Technology).
The difference comes here, In UG course you study all the fields and scope of your branch, while in PG course you have to opt a particular field from your branch. In simple words, you have to choose your field to get specialization in PG course.

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Well ug means undergraduate studies where you learn all areas of particular branch whereas pg means post graduate where you select a particular area in your branch to study further in detail. For example in ug mechanical you study basics of 1) thermodynamics and fluid mechanics​ 2) design of machines 3) manufacturing and production but in m tech you have to select a specific area from above to study further.

Dear Omkar

UG(Under Graduation) which is for 4 years after which you can do PG(Post Graduation) which is for 2 years. Once you complete UG you can apply for PG course.

UG means Undergraduate course which you will do after 12th class I.e BTech in case of engineering.

PG is postgraduate course that you will do after Btech I.e MTech. Mtech is postgraduate course. Some engineer students do MBA after Btech which is also postgraduate course. Mtech is mostly Oriented towards research work . Most of the students do Mtech for research, teaching purposes , but you can also get job after Mtech also.

Ug is under graduate course be or btech.Pg means post graduate degree mtech.So firstly you have to get ug degree only after that you can apply for pg.

UG= Under Graduate course. In Engineering there are B.tech degree. B.tech can done in various domain like computer science, electronics, electrical. In B.tech three are mainly 2 sector.
One is IT sector and another is Core sector. In IT sector there are many courses. Like CSE, IT, ECE,EEE.
In core sector there are many courses like CIVIL, EE, ME etc.

PG= Post Graduate course. After the graduation in any domain . One can do his/ her masters from any where he/she might get.

B.E is bachelor in engineering and B.Tech are UG courses in engineering and
M.E and M.Tech is PG courses in engineering.
Some do M.S abroad is some subject.