To decide which words to include in the dictionary and to determine what they mean, Merriam-Webster editors study the language as it's used. They carefully monitor which words people use most often and how they use them.
Each day most Merriam-Webster editors devote an hour or two to reading a cross section of published material, including books, newspapers, magazines, and electronic publications; in our office this activity is called "reading and marking." The editors scour the texts in search of new words, new usages of existing words, variant spellings, and inflected forms–in short, anything that might help in deciding if a word belongs in the dictionary, understanding what it means, and determining typical usage. Any word of interest is marked, along with surrounding context that offers insight into its form and use.

What do you mean by "the dictionary"? There is not one central dictionary. Each one has their own rules.

Any of the major dictionaries. Eg. Oxford English and other equivalents.

Somebody needs to throw an entry up on urban dictionary too if it isn't already on there

Lol, someone should ask The Foundation Foundation to set one up.

Always thought bitgold would have been better. "Coin" suggests "currency", but then again "gold" suggests "physical".