Master label is a custom name given to a lightning web component. Developers can given user-friendly name and that name will be visible in the Lightning App Builder and in Experience Builder.
Sample meta.xml code-
<apiVersion>42.0</apiVersion>
<isExposed>true</isExposed>
<masterLabel>MyLWCComponent</masterLabel>
<targets>
<target>lightning__RecordPage</target>
<target>lightning__AppPage</target>
<target>lightning__HomePage</target>
</targets>
So next time when you add a lightning component in a page, search Master Label(
MyLWCComponent) in App builder.
Let me know your thoughts in the comment section!!