In gameplay terms, an Engraving adds a certain bonus to your equipment. The better the Engraving, the higher the bonus. There are a lot of different types in the game that offer different bonuses. Examples include increased health or damage.
Not every type of Engraving can be applied to every type of equipment. Some work on melee weapons only, for example.
Engravings unlock once you complete certain actions in the game, like quests or challenges. You can see the unlock requirements of an Engraving in the list explained later on in the article.
To apply an Engraving, you need a blacksmith. Visit any blacksmith in-game and talk to them to access the Engrave option.
If you select a piece of equipment that already has an Engraving, you can replace it by applying a different one. A new Engraving will always replace a previous one, the effects do not stack.
You can check all Engravings that are available to you and which ones are currently applied to your weapons and armour by opening your Inventory and selecting Engrave.
This overview will also show you the requirement for Engravings that are still locked as well as your progress towards them.