Canvassing [canvass (verb)] is the systematic initiation of direct contact with a target group of individuals commonly used during political campaigns.

A campaign team (and during elections a candidate) will knock on doors of private residences within a particular geographic area, engaging in face-to-face personal interaction with voters. Canvassing may also be performed by telephone, where it is referred to as telephone canvassing. The main purpose of canvassing is to perform voter identification – how individuals are planning to vote – rather than to argue with or persuade voters. This preparation is an integral part of a ‘get out the vote’ operation (GOTV), in which known supporters are contacted on polling day and reminded to cast their ballot.
ref: Wikipedia