Posting is the term Formever gives to a single post to the General Ledger. A posting is a hidden form with only two fields: a quantity of a currency and a form reference to a General Ledger account form.
The amount is signed with a negative being a Credit and a positive amount is a Debit.
When a transaction is filed the posting procedure for the form and any detail lines are run. These procedures generate a set of Postings. The sum of all the amounts across all the Postings must be zero. i.e. the transaction must post a balanced set of Postings.