**Linux kernel** is a free, open-source, monolithic, modular, Unix-like operating system kernel. It is the main component of the Linux operating system (OS) and is the core interface between the computer's hardware and its processes.  

> The **kernel** is a computer program at the core of an operating system (OS). It is the part of the OS that loads first and remains in the main memory. The kernel connects the system hardware to the application software.  

The Linux kernel is used by Linux distributions alongside GNU tools and libraries. This combination is sometimes referred to as GNU/Linux. Popular Linux distributions include Ubuntu, Fedora, and Arch Linux.

# Open-source
The Linux kernel was created by Linus Torvalds and is currently an open-source project with thousands of developers actively working on it.  

# Monolithic
The Linux kernel is monolithic, meaning the kernel handles all hardware and driver operations. The entire operating system is virtually working in kernel space.  

# Modular
The Linux kernel supports the insertion and removal at runtime of loadable kernel modules.  By keeping only the necessary modules in kernel memory, the kernel's memory footprint is reduced and its overall performance is increased. 

What is Linux kernel?

Open-source

Monolithic

Modular