These terms can have different meanings at different companies. To participate in your ESPP, you need to enroll. Depending on your company's procedures, you do this in a printed form or on a website.
Alert: If your company has multiple locations in different time zones, confirm the time of day and the time zone used for the enrollment deadline.

The enrollment date can be either the first day of the enrollment period or the enrollment deadline, depending on how your company (or outside stock plan provider) uses the term. The enrollment date can also be called the grant date. The maximum number of shares you purchase needs to be fixed by this date to avoid potential problems. The offering date is the first day of the offering period, which can also be the enrollment deadline.

See a related article on all of the key dates and terms you must know before you participate in an ESPP.