The encyclopedia wand is a device mentioned in Haruki Murakami's seminal science fiction novel, Hardboiled Wonderland and The End of the World. I do not know if the book is the true locus classicus of the idea, but I can't find a reference for it elsewhere, and it seems likely enough that Murakami's inventive mind would have originated the idea.
How the encyclopedia wand could theoretically encode any amount of data by inscribing a single point on a rod of some sort. The way this would be done is by first taking a piece of text and encoding it in some form, such as taking the word "word" and encoding it as 2415184 (in the interest of brevity, let aside the technicality of how to distinguish this from BDAEAHD, as well as how to encode punctuation and various other character sets). However large the string ends up being, just put a decimal point in front of it, and then using some type of laser, notch a point on your rod at that point. So, for example, the word "word" would be notched .2415184 of the way up the stick. Whatever the length of text. it can be compressed this way and then inscribed as a single point on a rod.

There are two possible problems with this: one is that even though the data is only physically cut in one place, the data only makes sense in the context of the total length of the stick. This in a way relates to atomic paradox: if you take the notch as an atomic point, it doesn't make any sense, it only makes sense in terms of the entire continuum of the stick. That point being rather philosophical, the practical problems with the encyclopedia wand need to be mentioned. As I said above, the word "word", which is, after all, only four letters long, would be encoded as .2415184, a seven digit number. If you were to take a meter long stick, that means that the notch would have to be 100 nanometers long. Using normal materials engineering, the smallest amount of material that could be notched on our encyclopedia wand is a single atom, which is one ten-billionth of a meter. This means that the amount of data that could be inscribed on a one meter stick would be, at most, ten characters. This sentence would not fit on an encyclopedia wand. If you were to go beyond normal materials engineering, perhaps by finding some unobtanium, you could get the encyclopedia wand to be notched down to the Planck length of 10^-39 meters, you would only be able to inscribe around 39 characters, perhaps less. on a one meter long stick. That means that even using this theoretical unobtanium construct, this paragraph would not fit on an encyclopedia wand.

So while the encyclopedia wand is a fascinating idea, and has a lot of meaning in terms of Murakami's book (although what that meaning could be is a matter of complicated hermeneutics), it doesn't not seem to be a practical reality.