Terrarium in simple words are plants in a glass container.
Oxford definitions define it as: a sealed transparent globe or similar container in which plants are grown.
Just as we have fishes in aquarium, we have plants in terrarium.
The word comes from the Latin terra (“earth”) + arium (a place or receptacle).
Terrarium May be of 2 main types: Open and closed.
A closed terrarium is a self-sustaining ecosystem that waters the plants through its own ecosystem- so there is no need to water the plants regularly in a well set ecosystem.

An open terrarium needs regular watering. Not all plants are suitable for closed terrarium.

If you’re looking for a desktop companion, a contemporary way to liven up your home, or a fun project to do with the kids – terrariums are a great option. They’re perfect for people like me who love the natural world, but live in the city with no garden and little space for plants. Or for people who’d like a stunning collection of exotic plants that require very little maintenance.
A terrarium is a perfect blend of art and science !
To get one for your self :