# Demand Flexibility: A Review of Quantification Methods, Models, and Required Data
## 3 Results
### Definitions of Key Terms  
Throughout the literature, various terms have been cited and defined when referencing topics related to demand-side management (DSM). This section will analyze the terms defined by the authors in this field. DSM was defined by [1; 6; 7; 8; 9; 10; 11] as encompassing any changes to customer electricity usage in response to the needs of the power grid. Across all studies reviewed, 12 different terms were used to refer to DSM or a subset of DSM, such as DR or demand flexibility. When reviewing the literature, many of the studies either defined DR [6; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27] or a term related to demand flexibility [1; 3; 22; 28; 29; 30] when referring to how customers can manage demand. These terms, DR and flexibility, seem to be used interchangeably throughout the literature, with DR frequently used to refer to programs implemented by utilities to manage and incentivize customer demand variations. Conversely, terms, including the word \"flexibility\" are used to broadly define any modification to power on the supply- or demand-side. Although there was no variation in terms referring to DR, terms defined by authors when referring to flexibility range significantly and include: \"flexibility\" [1; 22; 28; 30; 31; 32], \"demand flexibility\" [33], \"load flexibility\" [3], \"building energy flexibility\" [29; 34; 35; 36], \"energy flexibility\" [35; 37; 38], \"EV flexibility services\" [39], and \"planning flexibility\" [40]. Each of these terms can be used to describe a particular process or type of flexibility. For example, demand flexibility would be different from supply flexibility. Notably, energy flexibility could encompass either supply- or demand-side flexibility. While some authors employ their own definitions of these terms, many cite standardized definitions. For example, the International Energy Agency (IEA) Energy in Buildings and Communities Programme (EBC) Annex 67 definition for \"building energy flexibility\" [41] was commonly cited [29; 34; 35; 36]. Both DR and flexibility are cited as being \begin{table}
\begin{tabular}{l l l} \hline \hline
**Key Terms** & & **Purpose** \\ \hline Set 1: “residential” OR “home” OR “house*” OR “industrial” OR “commercial” & Define sector scope \\ Set 2: “building” OR “district” OR “community” OR “grid” OR “microgrids” & Define aggregation level \\ Set 3: “energy flexible” OR “demand flexible*” OR “load flexible*” OR “operat” & \multicolumn{1}{l}{} \\ OR “demand response” OR “DR” OR “load shift*” OR “load shed*” OR “load shav*” & \\ OR “load reduc*” OR “demand-side management” OR “demand side management” & Specify demand-side flexibility \\ OR “DSM” OR “load modular*” OR “load curtailment*” OR “demand curtailment*” & \\ OR “direct load control” OR “peak shav*” & \\ Set 4: “measure” OR “quanti*” OR “potential” OR “estimate*” OR “calculate*” & \\ OR “evaluat*” OR “defin*” & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Table describing each set of key terms included in the database search. An asterisk (*) allows for variability at the end of the term. For example “energy flexible*” allows the search to include “energy flexible” and “energy flexibility”. broad categorizations of activities in which customers can match their demand with grid resources to support activities such as grid planning or decreasing emissions. Based on this review, Figure 1 displays the relationship between DSM and DR including examples of the different types of DR defined and studied in various papers. Specifically, Ref. [22] defines two types of DR, incentive-based and price-based. Incentive-based DR refers to programs that offer an incentive, oftentimes monetary, to decrease customer demand during times of grid stress. On the other hand, price-based DR refers to electricity prices that influence customer demand on a continual basis. This definition is similar to the Federal Energy Regulatory Commission (FERC) definition of DR [42] cited by [16; 19], which generally defines two DR categories.