The difference between the two lies in the geocoding process. The address you provide is broken up into multiple representations of that address. For example, "12 Concorde Place, Toronto, ON" could have the following representations:
- 12 Concorde Place, Toronto, ON
- Concorde Place, Toronto, ON
- Toronto, ON
- ON
Each representation is searched for in the address locator (or in some cases against many locators). Each search produces a list of candidates, each having a match score. This match score represents how closely the search string matched the value in the locator. These candidates are then ranked against each other according to their match score and the accuracy of the locator/representation.
Continuing with the example from above, both "12 Concorde Place, Toronto, ON" and "Toronto, ON" could generate a match score of 100 since the full address was matched to a street address and the city was matched against a point or polygon for the city. However, the street address match is clearly superior and would get a higher candidate score.
This is just one example of what could affect the match and candidate score, but it should help you wrap your head around this obscure concept.