TLDR : These are 10 drops of XRP transactions Payburner creates when an account is imported.  1 drop of XRP is equal to 1/1000000 of an XRP.  At the current XRP/USD rate, this is the equivalent of 0.000020 USD. 

To see these transactions, turn off filtering by toggling the Filter switch on the main XRP Transactions view.

For a full explanation of these keys, click here.