GeoJSON and twitter
This metadata contains not just tidy numerals like "25" but also whole new sets of name/value pairs--big weird trees of data. A good example is in the "coordinates" part of the tweet. This value contains geographical information--latitude and longitude--in a format called GeoJSON, a dialect of JSON that's used to describe places. This can seem complicated at first, but it's actually awesome, because it means that simple-to-understand formats such as JSON can express some pretty complex ideas about the world. GeoJSON isn't controlled by Twitter; it's a published, open standard.
Twitter has added another field, called "place." Places are not just dots on a map but "specific, named locations." They include multiple coordinates--they actually define polygons over the surface of the earth. A tweet can thus contain a very rough outline of a given nation. A few tweets can, with some digital fiddling, serve as a primitive atlas. And through some slightly complex math, they can reveal how far one tweeter is from another. Tweets also have a "created_at" field, which indicates the exact time at which they were posted.
A simplified version of JavaScript called JSON, which stands for JavaScript Object Notation. API essentially means "speaks (and reads) JSON." The language comes in a bundle of name/value fields. In twtitter, 31 such fields of which make up a tweet. For example, if a tweet has been "favorited" 25 times, the corresponding name is "favorite_count" and "25" is the value.