Q.A company's HR department keeps a spreadsheet listing the names and employee codes of all 3,000 employees, from which 150 employees are to be selected for a survey. This spreadsheet is an example of:

Population (Universe) is the complete, well-defined set of all units about which information is sought; it may be finite (all shops in a taluka) or very large (all transactions on a payment app in a year). Sample is a smaller, representative part of the population, actually selected and studied to draw conclusions about the whole.

Related terms: a sampling unit is the individual element that can be selected (a customer, a household); the sampling frame is the actual list or record from which units are drawn (a customer database, an electoral roll); a parameter is a numerical characteristic of the population (e.g., population mean $\mu$); a statistic is the corresponding numerical characteristic computed from the sample (e.g., sample mean $\bar{x}$), used to estimate the parameter.

Example: a company's 20,000 registered customers form the population; 500 customers chosen for a spending survey form the sample, and the spreadsheet listing all 20,000 customers is the sampling frame.