Is there a common term for source and destination?

Depends on the type of source or destination. For example, if the source and destination are accounts, then a few folks already suggested "account". If the source and destination are companies, individuals, etc., then you use or prefix "partner", "foreign", "customer" or similar words with some indication of the type of source/destination. If it's a computer system, "partner" might still work, e.g.:

• "Partner", "PartnerEntity", "PartnerAccount", ...
• "Foreign", "ForeignEntity", "ForeignAccount", ...
• "TransactionEntity", "TransactionAccount", ...
• "TransferEntity", "TransferAccount", ...

In a computer system, especially in databases, people sometimes prefer longer names too, such as "SourceOrDestinationAccount" and usually another column elsewhere gives an indication whether its a source or destination. I prefer longer names to ensure clarity, so I could name it this way.

Hopefully, one of these will help...

station- a regular stopping place on a public transportation route.

so a station can be an origin or a destination.

also:

terminal- A departure and arrival building

Balance

..But with a qualifier:

• [Multi_Balance]
• [Running_Bal]
• [Ongoing_Bal]
• [Provisional_Bal]
• [Composite_Bal]
• [Conglomerate_Bal]
• [Interim_Bal]
• [Transient_Bal]
• [Provisional_Bal]
• [Shift_Account]
• [Reposition]
• [Flux]
• [Interchange]
• [Medley]
• [Olio] …

I believe that "account" would be a typical description. The word is both generic, as in "accounting," and specific, as in "house account," or "escrow account." For instance, an account at a bank or brokerage is an entity unto itself, with a name, and defining characteristics, such tax status, joint or individual ownership, etc. The various accounts within the banking and brokerage systems become waypoints as money clears from payer account, through the clearing houses, to payee account.