Qalb is an Arabic word that means "heart." Not like the red, beating organ in our bodies, but more like the center of our feelings and thoughts.
Just like how we have a physical heart that pumps blood and helps us stay alive, our qalb helps us feel emotions and think about things. When we feel happy or sad, or when we think about things that matter to us, it's our qalb that's doing the work.
The qalb is very important in many religions, especially in Islam. Muslims believe that the qalb is where the faith in Allah (God) resides and where we can connect with Him. If our qalb is pure and clean, we can understand His messages and feel peace and contentment.
So, to sum it up, qalb is the Arabic word for heart that refers to the center of our emotions and thoughts, and in Islam, it is believed to be the place where faith in Allah resides.