Please everybody, it's great to write tag wikis.
But read the guidelines first!
If the tag has an unusual name or meaning most people don't already know, then it's find to define the term in the tag wiki. Same if people are prone to misunderstand it. Or sometimes even why we chose a particular tag name over other possibilities.
It is NOT HELPFUL and it is AGAINST the Stack Exchange tag wiki guidelines to put in definitions of common everyday words like "money" and "bank".
Money is any financial instrument accepted as form of payment for good and services.
Tag wikis are there so you can instruct users on what kinds of questions the tag covers and how to use it, what kinds of questions under that topic are off-topic for our site, etc.
Blog post from 2011 by Jeff Atwood, our Stack Exchange overlord on this topic.
- Avoid generically defining the concept behind a tag, unless it is highly specialized.
Meta topic on this subject from 2013.
Please add other official links about tag wiki writing if you find some I missed.