Employer-specific and open work permits

According to IRCC, Canada has two types of work permits: employer-specific and open. Knowing which one you have tells you what you can and can't do.

Employer-specific work permits

Let you work under the conditions on the permit until it expires.
The permit shows the employer, location and occupation (Additional Information), a numbered list of conditions (Conditions), and any extra notes (Remarks).
You must comply with everything on the permit.
To apply: a job offer from an employer not on the non-compliant list, and the general work permit requirements.
Most jobs need an LMIA; some categories are exempt (for example C16 for French speakers outside Quebec).

Let you work for any employer in Canada, except non-compliant employers and businesses that regularly offer striptease, erotic dance, escort services or erotic massage.
No job offer is needed to apply; the employer doesn't need an LMIA, a job offer submission or a compliance fee.
According to IRCC, most people applying from outside Canada can't get an open work permit. They are only issued in specific situations.

Graduates (PGWP) and IEC Working Holiday participants.
Some family members: of permanent residence applicants, of work permit holders (with conditions), spouses of international students (with conditions).
Vulnerable people: refugees, victims of workplace abuse.
People waiting for permanent residence (bridging open work permit) and certain other cases.

Type of work: for example, a medical exam may be needed for some jobs.
Location: for example, an open work permit under the provincial nominee class may limit you to that province.

Note If you need a work permit and don't have one, you can't legally work in Canada or state on a job application that you are allowed to work.