Sealer is a kind of primer. Primers are substances that are formulated to adhere well to the surface of the underlying layer and create a uniform surface without any pores for the application of the final coating. Primers are used before painting wooden surfaces and walls. With their help, you can cover all kinds of defects and seams on the wood surface.
In simple terms, sealer can also be called a protective layer that makes the wood or wall surface resistant to damage during the painting process. It is natural that when the paint is applied on the surface of the wood, the moisture and chemicals in it can penetrate the structure of the wood and cause changes in it. Sealer prevents this from happening. In the production of sealer, oil, paint and polish are used.