Glossary of Key Terms

This glossary provides definitions for key terms used throughout the Biodiversity & Infrastructure Handbook, supporting consistent understanding across disciplines such as ecology, engineering, transport planning and policy.

Definitions are based on legal texts, reference documents and expert agreement, and cover essential concepts related to wildlife and traffic, habitat fragmentation, ecological connectivity, mitigation measures, monitoring, green infrastructure and nature-based solutions. The glossary helps practitioners interpret technical guidance and supports clear communication between stakeholders involved in infrastructure projects.

If you are new to transport ecology or working in a multi-disciplinary team, the glossary can serve as a quick reference before exploring detailed handbook chapters. Terms will continue to evolve as the handbook is updated through expert collaboration and user feedback.

Last update: October 2023 – How to cite

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There are currently 4 names in this directory beginning with the letter O.
Offset
Measurable conservation outcomes resulting from actions designed to compensate for significant residual adverse biodiversity impacts arising from development plans or projects after appropriate prevention and mitigation measures have been taken. The goal of biodiversity offsets is to achieve no net loss and preferably a net gain of biodiversity on the ground with respect to species composition, habitat structure, ecosystem function and people’s use and cultural values associated with biodiversity.
Openness Index
Relation between section and length of an underpass (wildlife passages or other type of transversal structures in roads, railways and waterways). To calculate this index, the cross-section (width*height) of the structure is divided by its length.
Operation and Maintenance
Fourth phase of the infrastructure life cycle. It is the next stage after the process of preparation and construction. It usually lasts for decades. During this phase, the infrastructure affects its surroundings with noise and light and pollution from traffic and maintenance, and it creates barriers to movement and splits species populations. See also 'Strategic Planning', 'Design', 'Construction', 'Decommissioning'.
Overpass
Structure, mainly roads or railways or other type of linear transport infrastrcuture (including its accesses) which allows vehicles, people or fauna, to cross above another transport infrastructure. See also 'Wildlife overpass'.