sampling target 

https://doi.org/10.1351/goldbook.08045
Portion of material, at a particular time, that the sample is intended to represent.
Notes:
  1. The sampling target should be defined prior to designing the sampling plan.
  2. The sampling target may be defined by Regulations (for example, lot size).
Source:
PAC, 2021, 93, 997. 'Metrological and quality concepts in analytical chemistry (IUPAC Recommendations 2021)' on page 1016 (https://doi.org/10.1515/pac-2019-0819)