Sometimes presented as inter parte (without the "s").
As between the members of a group only; two or more.
A legal relationship which is between specified parties only and does not concern others.
Most contracts are inter partes and indeed (no pun intended), often stipulate this in the preamble as in:
"This contact is between Jane Doe, Internet User, and the Duhaime Legal Information Corporation."
Statutes, as legal documents, are not inter partes, as they oblige upon everyone, the population at large.
Concerning law suits, judges sometimes speak of inter partes as referring to the parties to the litigation. For example, costs are only available inter partes.
In that context, an inter partes hearing is a hearing to which is convened the parties to the litigation.