Payroll refers to several things.
1) The list of all the employees of the company, including their individual salaries. If, for example, the company is a small one and the employees are few, it can be said that the company has a short payroll.
2) The amount of money that spent on the salaries of all the employees in a company. When used in this sense, one can say that a company has a large or small payroll, depending on the amount that is involved.
3) All the financial documents dealing with the above mentioned usages. When used in this general way, the payroll includes more than the salary. This also covers other items such as wages, deductions (taxes, medical insurance premiums, loans, and the like), bonuses, and the net pay of each employee.
The payroll period depends on the convention followed by the company. This can also depend on the location. Some companies have a bi-weekly payroll period. Others have a monthly payroll period. There are even companies which have a payroll period that covers one working week. Whichever convention a company follows, the end of one payroll period is always a welcome time for employees.