Open orders refers to your maker limit orders that are waiting in the order book to be matched and filled.
The maximum number of orders you can have open at any given time (across all trading pairs) is determined by your Verification level.
You have 45 buy limit orders and 14 sell limit orders on XBT/EUR and ETH/EUR. The orders have not yet been filled, bringing the total to 59 open orders.
You want to place a few more orders, but you are only verified to Starter level. The maximum limit for open orders for Starter accounts is 60.
This means that you can only place one more order that stays open before you reach the maximum number of open orders.