What is kerning? What is the difference between optical and metrics kerning?

What will be an ideal response?

Kerning makes text easier to read by adding or subtracting space between pairs of characters. Just looking at the text on a page, you can probably see that some character pairs are closer together than others based on the shapes of the characters. Many of the font families you will work with come with predefined kern pairs that handle letter pairings that might otherwise be problematic. For example, the letter W might be kerned differently when paired with the letter o than when paired with the letter i simply for readability. When this kerning is built into a font family, it’s called metrics kerning. However, some fonts don’t have built-in kerning, or they have kerning for some character pairs but not others. When this is the case, you can choose the optical kerning option in Photoshop, and Photoshop will adjust the spacing between character pairs based on the shapes of the characters. To work with metrics and optical kerning, you can choose either Metrics or Optical, rather than a number setting, from the “Set the kerning between two characters” list on the Character panel.