Libraries for computational codes

Libraries are the files are the executable files which are used by other executable/code/applications. It can be classified in to two types.

Static
Shared

Writing a code without any dependencies is a huge challenge, the application size would be huge. Libraries come in handy when you deal with large application.

Even the basic commands such as pwd, ls, cp, etc. See here the example.
To see the libraries that are used by a particular executable, use ldd.

ldd executable_name

ldd pwd

ldd ls

ldd cp

All these executable use many libraries. Likewise, if  you take any complex code, it would be depend on many libraries