MySql: What is Tablespace and why is it used?

While investigating an issue I came across this error,

30503 [ERROR] InnoDB: Attempted to open a previously opened tablespace. Previous tablespace mysql/innodb_index_stats uses space ID: 2 at filepath: ./mysql/innodb_index_stats.ibd. Cannot open tablespace Mydb/be_command_log which uses space ID: 2 at filepath: ./Mydb/be_command_log.ibd

After reading a bit about this issue I came to know that this is the known issue of mysql, https://bugs.mysql.com/bug.php?id=68267

But my problem is, I don't know much about how tablespace really works? and how is it useful?

As far as definition is concerned I read it from this link, https://en.wikipedia.org/wiki/Tablespace but it does not give all the information.

Can someone share some detailed information about what are tablespaces and how do they work?

Note:- I am currently using v5.6.15

Cheers!