Reserved funds (not to be confused with "reserved" funds on the exchange) are funds that were acquired by the bot earlier but are not yet sold. These funds are reserved for this specific trade pair (market) with the intention to sell them there. Note that this is even so when the market is currently not selected so they will not be used as a base currency on another market.
These reserved funds can easily be "released": Via the menu, select "Orders" and then scroll down to "Accumulated Funds (order history)" and click "RELEASE FUNDS".
A list of the original buy orders will be shown. You can select one or more of them to match the total quantity you would like to release and then click "Confirm".
Consider the following example to clarify things further: suppose 0.1 ETH was acquired on Bittrex:ETH/BTC. Then that amount of ETH would be "reserved" on Bittrex:ETH /BTC only. Hence, this amount of ETH would not be available as a base currency on, for example, ADA/ETH