What does the small-print number surrounded by parentheses next to a Counterwallet token balance mean?

It looks like this:

The smaller number shows the current token balance at this address including unconfirmed transactions.

Typically you will see this if you send tokens or create a DEx order.

In this particular case the number surrounded by brackets is slightly larger, which means it’s an incoming transaction.
Specifically, a small amount of XCP was sent to this address, but since each Counterparty transaction includes a dust amount of bitcoin, this pending transaction reflects the increased amount of BTC at the address that will be final once the transaction is confirmed (included in the blockchain.)

Why does Counterwallet not “finalize” such transactions sooner? Because not every transaction succeeds (gets confirmed).