# Definitions Sustainability encompasses seven focus areas: + [Region selection](region-selection.md) + [Alignment to demand](alignment-to-demand.md) + [Software and architecture - optimization](software-and-architecture-optimization.md) + [Software and architecture - cloud](software-and-architecture-cloud.md) + [Data management](data-management-sus.md) + [Hardware and services - optimization](hardware-and-services-optimization.md) + [Hardware and services - power management](hardware-and-services-power-management.md) + [Process and culture - user guidance](process-and-culture-user-guidance.md) The following is a list of sustainability-specific definitions in the IoT Lens. + **Energy efficiency or power efficiency**: Used interchangeably in this document. + **Truck roll (or site visit):** The act of sending a technician to a site to resolve an issue. This has impacts both from an [operational cost perspective](https://www.tsia.com/press-releases/2012/soaring-field-service-costs-demand-investments-in-process-technology) (technician labor, fuel costs, maintenance running to hundreds of dollars per device) as well as [carbon footprint](https://nepis.epa.gov/Exe/ZyNET.exe/P100JPPH.TXT?ZyActionD=ZyDocument&Client=EPA&Index=2011+Thru+2015&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C11thru15%5CTxt%5C00000011%5CP100JPPH.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL) (emissions, wear and tear). Consequently, designing IoT devices to minimize the need for truck rolls is a key imperative. + **Battery life:** Refers to how long a device can run on a single charge. + **Battery lifetime:** Refers to how long the battery can be in operation before needing replacement.