Single and double spacing in text
On the web, the two settings that apply here are "line-height", which is the space between each line of text, and then "margin", which is the space between each new paragraph (a new paragraph is created when you hit ENTER). Since each setting can be tweaked independently, it's harder on the web to talk about what "single" or "double" spacing actually means. For example, you can have small line-height, and then a large paragraph margin, or vice versa.