Minecraft wiki entry for Other_data_format, associated text: : Parent tag.
 Command: The command entered into the command block.
 Version: The data version.
 SuccessCount: Represents the strength of the analog signal output by redstone comparators attached to this command block.
 CustomName: The custom name or hover text of this command block.
 LastOutput: The translation key of the output's last line generated by the command block. Still stored even if the gamerule commandBlockOutput is false. Appears in the command GUI.
 LastOutputParams: The params for the output's translation key.
: A param.
 TrackOutput: Determines whether the LastOutput is stored. Can be toggled in the GUI by clicking a button near the "Previous Output" textbox.
 LastExecution: Stores the time when a command block was last executed.
 TickDelay: The delay between each execution.
 ExecuteOnFirstTick: True if it executes on the first tick once saved or activated.