What is the difference between employee and personnel?

A basic difference is that personnel refers to many people and employee refers to one individual.

Oftentimes, in a company, there will be a "personnel department" that handles employment, benefits, hiring, and other tasks related to the employees of the company. "Personnel department" is also known as "Human Resources" or "HR." Some temporary employment agencies refer to themselves as a "personnel staffing solution."

In sentences:

1) My boss said that he appreciated having me as his employee. 2) During the holiday season, there is a normal reduction in personnel in most companies.

I guess the question is about Personnel and Employees (plural of 'employee').

Employees are all the people that are working under a company.

While

Personnel are all the people working for a company.

This make a big difference.

Personnel include "Affiliates, officers, directors, employees, agents, contractors, consultants, vendors, internals, invitees and representatives".

While Employees doesn't include independent contracts but just "employees". I suppose a freelancer can be considered personnel but not employees.