CSS padding is a property used to create space around the content inside an element. It defines the amount of space between the element's content and its border. Padding can be set for each side (top, right, bottom, left) individually or using a shorthand notation. For example:
```css
.element {
padding: 10px; /* applies 10px padding to all sides */
padding-top: 5px;
padding-right: 15px;
padding-bottom: 5px;
padding-left: 15px;
}
```
You can also use percentages, pixels, ems, rems, or other units to define padding values. Shorthand notation follows the order: top, right, bottom, left. For example:
```css
.element {
padding: 10px 20px 15px 5px; /* top, right, bottom, left */
}
```
Remember that padding increases the total size of the element, affecting its overall dimensions within the layout.