What are Custom Labels and how are they used in Apex and LWC?

Custom Labels are reusable text values defined in Setup that can be used across Apex, Visualforce, and LWC. They support translation — you can define different values per language, enabling multi-language applications. In Apex: System.Label.MyLabel. In Visualforce: {!$Label.MyLabel}. In LWC: Import with import LABEL_NAME from '@salesforce/label/c.MyLabel'; and reference as a property. Use custom labels for: UI text strings, error messages, success messages, and any text that may need to be translated or updated without a code deployment. Labels can also be used in Flows, formula fields, and validation rules. Maximum 5,000 custom labels per org.