A thin client is a simple computing system which drives a keyboard and display and connects to the Internet or Wireless phone service for most software functions, for example email and text editing. Thin means lacking local software. Client means that the simple computer acts as a client of a software provider which serves the software functions from another location.
Typically, one needs a user account with a service provider which owns and operates the software used.
Because the thin client does not contain the data or information used, it should be considered insecure. In some cases the software provider may have a license which specifies that the service provider retains copyright of documents produced. It is always wise to read the service agreement carefully!