Reuse the best practices and know-how capitalized from existing Software Process Models is a promising approach to model high quality Software Processes. This paper presents a part of an approach for software processes reuse based on software architectures. This contribution is based on exploiting Software Process know-how and the solution proposed after the study of existing work on software process reuse field, our study focuses on approaches for reusing based on software architectures and based on domain ontology. AoSP (Architecture oriented Software Process) approach, deals with the engineering "for" and "by" reusing Software Processes, it exploits the progress of two research fields that promote reusing for the Software process reusing: domain ontologies and software architectures. AoSP exploits an domain ontology to retrieve, describe and deploy software process architectures. This article details the engineering "for" reusing SPs step of AoSP, it explains how the software process architectures are described and discusses the software process ontology conceptualization and Software Process knowledge acquisition is done.