Based on TOGAF®, a solution architecture is “a description of a discrete and focused business operation or activity and how information systems / technical infrastructure supports that operation.
A Solution Architecture typically applies to a single project or project release, assisting in the translation of requirements into a solution vision, high-level business and/or IT system specifications, and a portfolio of implementation tasks”.

Within the context of the EIRA©, the solution architecture describes the specific architecture of a solution. It can be derived from a solution architecture template.

Source: European Interoperability Reference Architecture (EIRA version 3) (url) (with information on the 3rd release at the website of the ISA² - Interoperability solutions for public administrations, businesses and citizens).