The employee stock purchase plan or ESPP is a benefits program run by companies that allows employees to purchase stock or shares of the company at a discounted price. The stocks or shares are often offered at a discount versus the market value of the share.
Employees can opt in to participate in the ESPP by commiting a % of their salary on a monthly basis. The plan has a stock purchase date were the funds contribute by the employees are being used to purchase the shares which later will be distributed to the employees.
You can find out about your ESPP plan by accessing your companies benefits page or contacting your HR team. In most cases information about the ESPP is included in the company's employee handbook.
There are tax efficienies in most ESPP programs and tend to vary by state for US based companies and by country for the rest of the world.
The main downside of the ESPP program is volatility of the stock price. Alghtough the shares will be purchased at a discounted price, the share price might drop below the purchase price at a future date.