In typography, leading ( /ˈlɛdɪŋ/) refers to the distance between the baselines of successive lines of type.
By this definition, isn't it the same thing as line height?
But in the following examples in the same wikipedia page, it seems leading is extra space between lines, not line height. Otherwise, "no leading" should mean "no line height" which is obviously wrong. And 50%/100% leading seems to mean adding an extra inter-line spacing of 50%/100% natural line height.
Wikipedia is not the only source that holds contradictory content. Another website in the first search result page of "font leading" also gives contradictory graphical demonstrations.
And if you are an iOS developer, you may know that UIFont has a property called leading which returns line height. The fact that the property is now deprecated and replaced by a new property call lineHeight further shows how confusing this leading thing is.
I'm inclined to think leading as extra space added between lines. And here are two references that support this understanding:
leading (pronounced: ledding) The amount of space added between lines of text to make the document legible. The term originally referred to the thin lead spacers that printers used to physically increase space between lines of metal type. Most applications automatically apply standard leading based on the point size of the font. Closer leading fits more text on the page, but decreases legibility. Looser leading spreads text out to fill a page and makes the document easier to read. Leading can also be negative, in which case the lines of text are so close that they overlap or touch.
kCTParagraphStyleSpecifierLineSpacing The space in points added between lines within the paragraph (commonly known as leading). This value is always nonnegative. Type: CGFloat. Default: 0.0. Application: CTFramesetter.
Maybe leading is really misleading. I hope someone can tell me definitely what exactly leading is. But maybe leading is just a typographic term that can never receive a consensus, thus should be avoided as much as possible, and even be deprecated in preference for more clear and compatible concepts such as ascent, descent, line gap, and line height(line height = ascent + descent + line gap).