CIP stands for Celesta Improvement Proposal. A CIP is a design document that describes a new feature or aspect of the core Celesta code, or the Celesta project, its processes, or its environment. A CIP provides a concise technical specification of the feature, describes the motivation for the change, and discusses the rationale behind the design.
CIPs are the primary mechanism for proposing major new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Celesta.
See CIP-1 for a description of CIPs and the CIP process.