what is lazy loading?

http://en.wikipedia.org/wiki/Lazy_loading

Just read it, its simple

In a nutshell: when an object (e.g. "User" containing basic info about username, account status) contains a reference to another object that is not always needed (e.g. UserProfile containing stuff like biography, birthplace etc.), the lazy loading helps you to save the resources in a way that it loads the object from the database only when referenced. Lazy loading is handled by Hibernate in a transparent, automatic way, so you theoretically don't have to take much care about it..

In other words, without lazy loading, fetching just one object could result in loading the entire database, and that's very bad.

Read the article, it is basically simple, but has a *lot* of gotchas and requires reading and experimenting.

Defer initialization of an object until the point at which it is needed. It can contribute to efficiency in the program's operation if properly and appropriately used. The opposite of lazy loading is Eager Loading.

For example when we query Users class...

from Users u; --retrieve users objects

May users object has refer some other objects like Profile, Messages etc.,
When we run the above query it only get Users object from table. When we refer Profile object that time only it loads Profile object from table. that technique is lazy loading. due to that it require only small time and space.