It signifies:
* Something immense contained within something small.
* A great deal of knowledge or ability packed into a small space or person.
* Having a vast potential or capacity despite seemingly limited resources.
For example:
* A young child who speaks multiple languages could be described as having a "gagar mein sagar" of linguistic abilities.
* A small village that boasts a rich cultural heritage could be said to have a "gagar mein sagar" of traditions.
The idiom is often used to express admiration for someone or something that has a vast amount of potential or capacity despite its seemingly limited size or scope.