Core Cash Target is the ideal amount you will have in your bank account before spending on new projects, paying shareholders, hiring new team members etc. It's calculated by adding your taxes due and two months worth of overheads for the current period.
The underlying calculations can be found by clicking on the tile and flipping it around to reveal the graphs and numbers in more detail.
If you select a finalised month (see red square above) that isn't the financial year end then the figures will be annualised for the current financial period.
The little coloured number (either red or green) at the base of the figure box, is the percentage points difference in the revenue growth between now and the previous financial year.