Both hydration and hydrate agents are working to ensure the moisture levels of our skin.
Our skin's natural lipid barrier protects against water damage and water loss, but if you have dry skin, flaky skin, you may need additional restoration, enter your moisturisers. Dry skin means that your skin does not produce enough lipid cells alone to help moisturise. On the other hand, moisturisers usually contain moisturisers.
It works to capture humidity from the air and saturate it in the skin layers.
So to what is the difference? Dehydrated skin essentially requires moisture. Oil and hydratation are necessary for the dry skin. When dealing with the exact issue, knowing the difference is key.