New (and not so new) developers may want to know the definition of various timestamp-related terms that we use in WT engineering and in our Jira discussions.  We should document this someplace (probably the Architecture Guide).

Three terms that come to mind are:

• Mixed mode timestamp
• Out of order timestamp
• Ghost timestamp (e.g., see SERVER-45147)

In addition to explaining the meaning, we should document the expected behavior from WT, and the use case(s) they are intended to support.