What is a Gem?

Gem is a ruby software package which offers particular functionalities to the ruby programs.

Basically, all the functionality a Gem provide we can build by ourselves. But since sometimes we don't have time to build the functionality step by step, and if there are some Gems can help us solve problems, we will choose to use those Gems instead of building a wheel.

But using more Gems means the dependency between different Gems may conflict. Also, more Gems may slow down your application. So you have to decide when to use a Gem and when is not.

Resource: What is a Gem