Usually, entries are not made with a call of "Pass", leaving it up to the client (bridge playing) program to calculate the best call when BidBase does not find a bid to make.
However, you will see some entries with "Pass" as the call. These are usually examples given in books and articles of hands which may look like they are worth a bid, but which are not, according to the experts. See the "Reference/Source" for more information about such hands.
If you create a new entry and your test hand for it gets trapped by one of these "Pass" entries when it is tested, it would be an excellent idea to rethink either your specs or your test hand or if possible, to check with the Reference given.
An entry for a Pass as discussed above should not be confused with entries for a Forcing Pass.