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.