No Parking
Motorists are only permitted to load or unload passengers or merchandise.  

No Standing
Motorists are only permitted to receive and discharge passengers. Typically used in the area of TTC bus stops.

No Stopping
Motorists are generally not permitted to stop for any reason except to avoid a conflict with other traffic or in compliance with the directions of a constable or other police officer or of a traffic control sign or signal.

Legal Definitions
The Toronto Municipal Code Chapter 950-501-J is part of article V - Parking, Stopping and Standing and refers to the Highway Traffic Act for definitions of park, stand, etc.

No Parking
Section 1(1) of the HTA defines park or parking where prohibited as: "the standing of a vehicle, whether occupied or not, except when standing temporarily for the purpose of and while actually engaged in loading or unloading merchandise or passengers"

No Standing
The same section defines stand or standing where prohibited as: "the halting of a vehicle, whether occupied or not, except for the purpose of and while actually engaged in receiving or discharging passengers"

No Stopping
The same section defines stop or stopping where prohibited as: "the halting of a vehicle, even momentarily, whether occupied or not, except when necessary to avoid conflict with other traffic or in compliance with the directions of a police officer or of a traffic control sign or signal;"

Delivery and Courier vehicles
Where parking is prohibited, motorists may stop while actively engaged in loading/unloading passengers and/or merchandise. However, motorists may not leave vehicles unattended if going into a building, etc.

Under Schedule VI (Commercial Loading Zones), sections of certain streets are designated as Commercial Loading Zones as marked by authorized signs. Commercial vehicles may stop while actively engaged in loading/unloading of passengers and/or merchandise and may not park/leave the vehicle unattended while they go into the building, etc.

Under Schedule IX (Delivery Vehicle Parking Zones), sections of certain streets are designated as Delivery Vehicle Parking Zones as marked by authorized signs. Parking while on delivery is limited to a specific time period, eg. 30 mins. Only a few City streets have designated Delivery Vehicle Parking Zones.

Currently a Courier Delivery Zone pilot project is underway in the City of Toronto. Courier Delivery Zones are clearly indicated by authorized signs on several streets in the downtown area. Parking while on courier delivery is limited to a specific time period e.g 15 mins/30 mins, period time limits are posted on authorized signs.

Otherwise, couriers and delivery vehicles are subject to the same rules and regulations as other motorists, as set out in various Municipal Code Chapters.