Open orders refers to your maker limit orders that are waiting in the order book to be matched and filled.  Scheduled orders are orders placed with a start time five seconds or more in the future and will count towards your maximum number of open orders.

The maximum number of orders you can have open at any given time (across each trading pair) is determined by your Verification level.  

Example

You have 45 buy limit orders and 14 sell limit orders on BTC/EUR and ETH/EUR.

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 place 15 more orders on BTC/EUR and 46 more open orders on ETH/EUR before you reach the maximum number of open orders on those pairs. On other pairs, you can place 60 orders each.